enable nullable annotations in the web project & related code (#837)

14 files changed, 260 insertions, 176 deletions

diff --git a/src/SMAPI.Toolkit/Framework/Clients/WebApi/ModEntryModel.cs b/src/SMAPI.Toolkit/Framework/Clients/WebApi/ModEntryModel.cs
index d5ca2034..4fc4ea54 100644
--- a/src/SMAPI.Toolkit/Framework/Clients/WebApi/ModEntryModel.cs
+++ b/src/SMAPI.Toolkit/Framework/Clients/WebApi/ModEntryModel.cs
@@ -1,5 +1,3 @@
-#nullable disable
-
 using System;
 
 namespace StardewModdingAPI.Toolkit.Framework.Clients.WebApi
@@ -11,15 +9,26 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.WebApi
         ** Accessors
         *********/
         /// <summary>The mod's unique ID (if known).</summary>
-        public string ID { get; set; }
+        public string ID { get; }
 
         /// <summary>The update version recommended by the web API based on its version update and mapping rules.</summary>
-        public ModEntryVersionModel SuggestedUpdate { get; set; }
+        public ModEntryVersionModel? SuggestedUpdate { get; set; }
 
         /// <summary>Optional extended data which isn't needed for update checks.</summary>
-        public ModExtendedMetadataModel Metadata { get; set; }
+        public ModExtendedMetadataModel? Metadata { get; set; }
 
         /// <summary>The errors that occurred while fetching update data.</summary>
         public string[] Errors { get; set; } = Array.Empty<string>();
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="id">The mod's unique ID (if known).</param>
+        public ModEntryModel(string id)
+        {
+            this.ID = id;
+        }
     }
 }
diff --git a/src/SMAPI.Toolkit/Framework/Clients/WebApi/ModEntryVersionModel.cs b/src/SMAPI.Toolkit/Framework/Clients/WebApi/ModEntryVersionModel.cs
index 9aac7fd3..a1e78986 100644
--- a/src/SMAPI.Toolkit/Framework/Clients/WebApi/ModEntryVersionModel.cs
+++ b/src/SMAPI.Toolkit/Framework/Clients/WebApi/ModEntryVersionModel.cs
@@ -1,5 +1,3 @@
-#nullable disable
-
 using Newtonsoft.Json;
 using StardewModdingAPI.Toolkit.Serialization.Converters;
 
@@ -13,19 +11,16 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.WebApi
         *********/
         /// <summary>The version number.</summary>
         [JsonConverter(typeof(NonStandardSemanticVersionConverter))]
-        public ISemanticVersion Version { get; set; }
+        public ISemanticVersion Version { get; }
 
         /// <summary>The mod page URL.</summary>
-        public string Url { get; set; }
+        public string Url { get; }
 
 
         /*********
         ** Public methods
         *********/
         /// <summary>Construct an instance.</summary>
-        public ModEntryVersionModel() { }
-
-        /// <summary>Construct an instance.</summary>
         /// <param name="version">The version number.</param>
         /// <param name="url">The mod page URL.</param>
         public ModEntryVersionModel(ISemanticVersion version, string url)
diff --git a/src/SMAPI.Toolkit/Framework/Clients/WebApi/ModExtendedMetadataModel.cs b/src/SMAPI.Toolkit/Framework/Clients/WebApi/ModExtendedMetadataModel.cs
index eb54ec78..272a2063 100644
--- a/src/SMAPI.Toolkit/Framework/Clients/WebApi/ModExtendedMetadataModel.cs
+++ b/src/SMAPI.Toolkit/Framework/Clients/WebApi/ModExtendedMetadataModel.cs
@@ -1,5 +1,3 @@
-#nullable disable
-
 using System;
 using System.Collections.Generic;
 using System.Linq;
@@ -23,7 +21,7 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.WebApi
         public string[] ID { get; set; } = Array.Empty<string>();
 
         /// <summary>The mod's display name.</summary>
-        public string Name { get; set; }
+        public string? Name { get; set; }
 
         /// <summary>The mod ID on Nexus.</summary>
         public int? NexusID { get; set; }
@@ -35,31 +33,31 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.WebApi
         public int? CurseForgeID { get; set; }
 
         /// <summary>The mod key in the CurseForge mod repo (used in mod page URLs).</summary>
-        public string CurseForgeKey { get; set; }
+        public string? CurseForgeKey { get; set; }
 
         /// <summary>The mod ID in the ModDrop mod repo.</summary>
         public int? ModDropID { get; set; }
 
         /// <summary>The GitHub repository in the form 'owner/repo'.</summary>
-        public string GitHubRepo { get; set; }
+        public string? GitHubRepo { get; set; }
 
         /// <summary>The URL to a non-GitHub source repo.</summary>
-        public string CustomSourceUrl { get; set; }
+        public string? CustomSourceUrl { get; set; }
 
         /// <summary>The custom mod page URL (if applicable).</summary>
-        public string CustomUrl { get; set; }
+        public string? CustomUrl { get; set; }
 
         /// <summary>The main version.</summary>
-        public ModEntryVersionModel Main { get; set; }
+        public ModEntryVersionModel? Main { get; set; }
 
         /// <summary>The latest optional version, if newer than <see cref="Main"/>.</summary>
-        public ModEntryVersionModel Optional { get; set; }
+        public ModEntryVersionModel? Optional { get; set; }
 
         /// <summary>The latest unofficial version, if newer than <see cref="Main"/> and <see cref="Optional"/>.</summary>
-        public ModEntryVersionModel Unofficial { get; set; }
+        public ModEntryVersionModel? Unofficial { get; set; }
 
         /// <summary>The latest unofficial version for the current Stardew Valley or SMAPI beta, if any.</summary>
-        public ModEntryVersionModel UnofficialForBeta { get; set; }
+        public ModEntryVersionModel? UnofficialForBeta { get; set; }
 
         /****
         ** Stable compatibility
@@ -69,10 +67,10 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.WebApi
         public WikiCompatibilityStatus? CompatibilityStatus { get; set; }
 
         /// <summary>The human-readable summary of the compatibility status or workaround, without HTML formatting.</summary>
-        public string CompatibilitySummary { get; set; }
+        public string? CompatibilitySummary { get; set; }
 
         /// <summary>The game or SMAPI version which broke this mod, if applicable.</summary>
-        public string BrokeIn { get; set; }
+        public string? BrokeIn { get; set; }
 
         /****
         ** Beta compatibility
@@ -82,22 +80,22 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.WebApi
         public WikiCompatibilityStatus? BetaCompatibilityStatus { get; set; }
 
         /// <summary>The human-readable summary of the compatibility status or workaround for the Stardew Valley beta (if any), without HTML formatting.</summary>
-        public string BetaCompatibilitySummary { get; set; }
+        public string? BetaCompatibilitySummary { get; set; }
 
         /// <summary>The beta game or SMAPI version which broke this mod, if applicable.</summary>
-        public string BetaBrokeIn { get; set; }
+        public string? BetaBrokeIn { get; set; }
 
         /****
         ** Version mappings
         ****/
         /// <summary>A serialized change descriptor to apply to the local version during update checks (see <see cref="ChangeDescriptor"/>).</summary>
-        public string ChangeLocalVersions { get; set; }
+        public string? ChangeLocalVersions { get; set; }
 
         /// <summary>A serialized change descriptor to apply to the remote version during update checks (see <see cref="ChangeDescriptor"/>).</summary>
-        public string ChangeRemoteVersions { get; set; }
+        public string? ChangeRemoteVersions { get; set; }
 
         /// <summary>A serialized change descriptor to apply to the update keys during update checks (see <see cref="ChangeDescriptor"/>).</summary>
-        public string ChangeUpdateKeys { get; set; }
+        public string? ChangeUpdateKeys { get; set; }
 
 
         /*********
@@ -113,7 +111,7 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.WebApi
         /// <param name="optional">The latest optional version, if newer than <paramref name="main"/>.</param>
         /// <param name="unofficial">The latest unofficial version, if newer than <paramref name="main"/> and <paramref name="optional"/>.</param>
         /// <param name="unofficialForBeta">The latest unofficial version for the current Stardew Valley or SMAPI beta, if any.</param>
-        public ModExtendedMetadataModel(WikiModEntry wiki, ModDataRecord db, ModEntryVersionModel main, ModEntryVersionModel optional, ModEntryVersionModel unofficial, ModEntryVersionModel unofficialForBeta)
+        public ModExtendedMetadataModel(WikiModEntry? wiki, ModDataRecord? db, ModEntryVersionModel? main, ModEntryVersionModel? optional, ModEntryVersionModel? unofficial, ModEntryVersionModel? unofficialForBeta)
         {
             // versions
             this.Main = main;
diff --git a/src/SMAPI.Toolkit/Framework/Clients/WebApi/ModSearchEntryModel.cs b/src/SMAPI.Toolkit/Framework/Clients/WebApi/ModSearchEntryModel.cs
index 8fe8fa2a..9c11e1db 100644
--- a/src/SMAPI.Toolkit/Framework/Clients/WebApi/ModSearchEntryModel.cs
+++ b/src/SMAPI.Toolkit/Framework/Clients/WebApi/ModSearchEntryModel.cs
@@ -1,6 +1,5 @@
-#nullable disable
-
 using System;
+using System.Linq;
 
 namespace StardewModdingAPI.Toolkit.Framework.Clients.WebApi
 {
@@ -11,37 +10,39 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.WebApi
         ** Accessors
         *********/
         /// <summary>The unique mod ID.</summary>
-        public string ID { get; set; }
+        public string ID { get; }
 
         /// <summary>The namespaced mod update keys (if available).</summary>
-        public string[] UpdateKeys { get; set; }
+        public string[] UpdateKeys { get; private set; }
 
         /// <summary>The mod version installed by the local player. This is used for version mapping in some cases.</summary>
-        public ISemanticVersion InstalledVersion { get; set; }
+        public ISemanticVersion? InstalledVersion { get; }
 
         /// <summary>Whether the installed version is broken or could not be loaded.</summary>
-        public bool IsBroken { get; set; }
+        public bool IsBroken { get; }
 
 
         /*********
         ** Public methods
         *********/
-        /// <summary>Construct an empty instance.</summary>
-        public ModSearchEntryModel()
-        {
-            // needed for JSON deserializing
-        }
-
         /// <summary>Construct an instance.</summary>
         /// <param name="id">The unique mod ID.</param>
         /// <param name="installedVersion">The version installed by the local player. This is used for version mapping in some cases.</param>
         /// <param name="updateKeys">The namespaced mod update keys (if available).</param>
         /// <param name="isBroken">Whether the installed version is broken or could not be loaded.</param>
-        public ModSearchEntryModel(string id, ISemanticVersion installedVersion, string[] updateKeys, bool isBroken = false)
+        public ModSearchEntryModel(string id, ISemanticVersion? installedVersion, string[]? updateKeys, bool isBroken = false)
         {
             this.ID = id;
             this.InstalledVersion = installedVersion;
             this.UpdateKeys = updateKeys ?? Array.Empty<string>();
+            this.IsBroken = isBroken;
+        }
+
+        /// <summary>Add update keys for the mod.</summary>
+        /// <param name="updateKeys">The update keys to add.</param>
+        public void AddUpdateKeys(params string[] updateKeys)
+        {
+            this.UpdateKeys = this.UpdateKeys.Concat(updateKeys).ToArray();
         }
     }
 }
diff --git a/src/SMAPI.Toolkit/Framework/Clients/WebApi/ModSearchModel.cs b/src/SMAPI.Toolkit/Framework/Clients/WebApi/ModSearchModel.cs
index 393391f7..a0cd9d4d 100644
--- a/src/SMAPI.Toolkit/Framework/Clients/WebApi/ModSearchModel.cs
+++ b/src/SMAPI.Toolkit/Framework/Clients/WebApi/ModSearchModel.cs
@@ -1,5 +1,3 @@
-#nullable disable
-
 using System.Linq;
 using StardewModdingAPI.Toolkit.Utilities;
 
@@ -24,18 +22,12 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.WebApi
         public ISemanticVersion GameVersion { get; set; }
 
         /// <summary>The OS on which the player plays.</summary>
-        public Platform? Platform { get; set; }
+        public Platform Platform { get; set; }
 
 
         /*********
         ** Public methods
         *********/
-        /// <summary>Construct an empty instance.</summary>
-        public ModSearchModel()
-        {
-            // needed for JSON deserializing
-        }
-
         /// <summary>Construct an instance.</summary>
         /// <param name="mods">The mods to search.</param>
         /// <param name="apiVersion">The SMAPI version installed by the player. If this is null, the API won't provide a recommended update.</param>
diff --git a/src/SMAPI.Toolkit/Framework/Clients/WebApi/WebApiClient.cs b/src/SMAPI.Toolkit/Framework/Clients/WebApi/WebApiClient.cs
index 56acb768..d4282617 100644
--- a/src/SMAPI.Toolkit/Framework/Clients/WebApi/WebApiClient.cs
+++ b/src/SMAPI.Toolkit/Framework/Clients/WebApi/WebApiClient.cs
@@ -1,5 +1,3 @@
-#nullable disable
-
 using System;
 using System.Collections.Generic;
 using System.Linq;
@@ -72,7 +70,8 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.WebApi
             client.Headers["Content-Type"] = "application/json";
             client.Headers["User-Agent"] = $"SMAPI/{this.Version}";
             string response = client.UploadString(fullUrl, data);
-            return JsonConvert.DeserializeObject<TResult>(response, this.JsonSettings);
+            return JsonConvert.DeserializeObject<TResult>(response, this.JsonSettings)
+                ?? throw new InvalidOperationException($"Could not parse the response from POST {url}.");
         }
     }
 }
diff --git a/src/SMAPI.Toolkit/Framework/Clients/Wiki/ChangeDescriptor.cs b/src/SMAPI.Toolkit/Framework/Clients/Wiki/ChangeDescriptor.cs
index 910bf793..5978803e 100644
--- a/src/SMAPI.Toolkit/Framework/Clients/Wiki/ChangeDescriptor.cs
+++ b/src/SMAPI.Toolkit/Framework/Clients/Wiki/ChangeDescriptor.cs
@@ -1,5 +1,3 @@
-#nullable disable
-
 using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
@@ -49,7 +47,7 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
         /// <summary>Apply the change descriptors to a comma-delimited field.</summary>
         /// <param name="rawField">The raw field text.</param>
         /// <returns>Returns the modified field.</returns>
-        public string ApplyToCopy(string rawField)
+        public string? ApplyToCopy(string? rawField)
         {
             // get list
             List<string> values = !string.IsNullOrWhiteSpace(rawField)
@@ -75,12 +73,12 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
             {
                 for (int i = values.Count - 1; i >= 0; i--)
                 {
-                    string value = this.FormatValue(values[i]?.Trim() ?? string.Empty);
+                    string value = this.FormatValue(values[i].Trim());
 
                     if (this.Remove.Contains(value))
                         values.RemoveAt(i);
 
-                    else if (this.Replace.TryGetValue(value, out string newValue))
+                    else if (this.Replace.TryGetValue(value, out string? newValue))
                         values[i] = newValue;
                 }
             }
@@ -88,7 +86,7 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
             // add values
             if (this.Add.Any())
             {
-                HashSet<string> curValues = new HashSet<string>(values.Select(p => p?.Trim() ?? string.Empty), StringComparer.OrdinalIgnoreCase);
+                HashSet<string> curValues = new HashSet<string>(values.Select(p => p.Trim()), StringComparer.OrdinalIgnoreCase);
                 foreach (string add in this.Add)
                 {
                     if (!curValues.Contains(add))
@@ -121,7 +119,7 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
         /// <param name="descriptor">The raw change descriptor.</param>
         /// <param name="errors">The human-readable error message describing any invalid values that were ignored.</param>
         /// <param name="formatValue">Format a raw value into a normalized form if needed.</param>
-        public static ChangeDescriptor Parse(string descriptor, out string[] errors, Func<string, string> formatValue = null)
+        public static ChangeDescriptor Parse(string descriptor, out string[] errors, Func<string, string>? formatValue = null)
         {
             // init
             formatValue ??= p => p;
diff --git a/src/SMAPI.Toolkit/Framework/Clients/Wiki/WikiClient.cs b/src/SMAPI.Toolkit/Framework/Clients/Wiki/WikiClient.cs
index 86c3bd75..7f06d170 100644
--- a/src/SMAPI.Toolkit/Framework/Clients/Wiki/WikiClient.cs
+++ b/src/SMAPI.Toolkit/Framework/Clients/Wiki/WikiClient.cs
@@ -1,5 +1,3 @@
-#nullable disable
-
 using System;
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
@@ -53,8 +51,8 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
             doc.LoadHtml(html);
 
             // fetch game versions
-            string stableVersion = doc.DocumentNode.SelectSingleNode("//div[@class='game-stable-version']")?.InnerText;
-            string betaVersion = doc.DocumentNode.SelectSingleNode("//div[@class='game-beta-version']")?.InnerText;
+            string? stableVersion = doc.DocumentNode.SelectSingleNode("//div[@class='game-stable-version']")?.InnerText;
+            string? betaVersion = doc.DocumentNode.SelectSingleNode("//div[@class='game-beta-version']")?.InnerText;
             if (betaVersion == stableVersion)
                 betaVersion = null;
 
@@ -65,7 +63,7 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
                 if (modNodes == null)
                     throw new InvalidOperationException("Can't parse wiki compatibility list, no mod data overrides section found.");
 
-                foreach (var entry in this.ParseOverrideEntries(modNodes))
+                foreach (WikiDataOverrideEntry entry in this.ParseOverrideEntries(modNodes))
                 {
                     if (entry.Ids.Any() != true || !entry.HasChanges)
                         continue;
@@ -85,18 +83,17 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
             }
 
             // build model
-            return new WikiModList
-            {
-                StableVersion = stableVersion,
-                BetaVersion = betaVersion,
-                Mods = mods
-            };
+            return new WikiModList(
+                stableVersion: stableVersion,
+                betaVersion: betaVersion,
+                mods: mods
+            );
         }
 
         /// <summary>Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.</summary>
         public void Dispose()
         {
-            this.Client?.Dispose();
+            this.Client.Dispose();
         }
 
 
@@ -118,71 +115,68 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
                 int? nexusID = this.GetAttributeAsNullableInt(node, "data-nexus-id");
                 int? chucklefishID = this.GetAttributeAsNullableInt(node, "data-cf-id");
                 int? curseForgeID = this.GetAttributeAsNullableInt(node, "data-curseforge-id");
-                string curseForgeKey = this.GetAttribute(node, "data-curseforge-key");
+                string? curseForgeKey = this.GetAttribute(node, "data-curseforge-key");
                 int? modDropID = this.GetAttributeAsNullableInt(node, "data-moddrop-id");
-                string githubRepo = this.GetAttribute(node, "data-github");
-                string customSourceUrl = this.GetAttribute(node, "data-custom-source");
-                string customUrl = this.GetAttribute(node, "data-url");
-                string anchor = this.GetAttribute(node, "id");
-                string contentPackFor = this.GetAttribute(node, "data-content-pack-for");
-                string devNote = this.GetAttribute(node, "data-dev-note");
-                string pullRequestUrl = this.GetAttribute(node, "data-pr");
+                string? githubRepo = this.GetAttribute(node, "data-github");
+                string? customSourceUrl = this.GetAttribute(node, "data-custom-source");
+                string? customUrl = this.GetAttribute(node, "data-url");
+                string? anchor = this.GetAttribute(node, "id");
+                string? contentPackFor = this.GetAttribute(node, "data-content-pack-for");
+                string? devNote = this.GetAttribute(node, "data-dev-note");
+                string? pullRequestUrl = this.GetAttribute(node, "data-pr");
 
                 // parse stable compatibility
-                WikiCompatibilityInfo compatibility = new()
-                {
-                    Status = this.GetAttributeAsEnum<WikiCompatibilityStatus>(node, "data-status") ?? WikiCompatibilityStatus.Ok,
-                    BrokeIn = this.GetAttribute(node, "data-broke-in"),
-                    UnofficialVersion = this.GetAttributeAsSemanticVersion(node, "data-unofficial-version"),
-                    UnofficialUrl = this.GetAttribute(node, "data-unofficial-url"),
-                    Summary = this.GetInnerHtml(node, "mod-summary")?.Trim()
-                };
+                WikiCompatibilityInfo compatibility = new(
+                    status: this.GetAttributeAsEnum<WikiCompatibilityStatus>(node, "data-status") ?? WikiCompatibilityStatus.Ok,
+                    brokeIn: this.GetAttribute(node, "data-broke-in"),
+                    unofficialVersion: this.GetAttributeAsSemanticVersion(node, "data-unofficial-version"),
+                    unofficialUrl: this.GetAttribute(node, "data-unofficial-url"),
+                    summary: this.GetInnerHtml(node, "mod-summary")?.Trim()
+                );
 
                 // parse beta compatibility
-                WikiCompatibilityInfo betaCompatibility = null;
+                WikiCompatibilityInfo? betaCompatibility = null;
                 {
                     WikiCompatibilityStatus? betaStatus = this.GetAttributeAsEnum<WikiCompatibilityStatus>(node, "data-beta-status");
                     if (betaStatus.HasValue)
                     {
-                        betaCompatibility = new WikiCompatibilityInfo
-                        {
-                            Status = betaStatus.Value,
-                            BrokeIn = this.GetAttribute(node, "data-beta-broke-in"),
-                            UnofficialVersion = this.GetAttributeAsSemanticVersion(node, "data-beta-unofficial-version"),
-                            UnofficialUrl = this.GetAttribute(node, "data-beta-unofficial-url"),
-                            Summary = this.GetInnerHtml(node, "mod-beta-summary")
-                        };
+                        betaCompatibility = new WikiCompatibilityInfo(
+                            status: betaStatus.Value,
+                            brokeIn: this.GetAttribute(node, "data-beta-broke-in"),
+                            unofficialVersion: this.GetAttributeAsSemanticVersion(node, "data-beta-unofficial-version"),
+                            unofficialUrl: this.GetAttribute(node, "data-beta-unofficial-url"),
+                            summary: this.GetInnerHtml(node, "mod-beta-summary")
+                        );
                     }
                 }
 
                 // find data overrides
-                WikiDataOverrideEntry overrides = ids
+                WikiDataOverrideEntry? overrides = ids
                     .Select(id => overridesById.TryGetValue(id, out overrides) ? overrides : null)
                     .FirstOrDefault(p => p != null);
 
                 // yield model
-                yield return new WikiModEntry
-                {
-                    ID = ids,
-                    Name = names,
-                    Author = authors,
-                    NexusID = nexusID,
-                    ChucklefishID = chucklefishID,
-                    CurseForgeID = curseForgeID,
-                    CurseForgeKey = curseForgeKey,
-                    ModDropID = modDropID,
-                    GitHubRepo = githubRepo,
-                    CustomSourceUrl = customSourceUrl,
-                    CustomUrl = customUrl,
-                    ContentPackFor = contentPackFor,
-                    Compatibility = compatibility,
-                    BetaCompatibility = betaCompatibility,
-                    Warnings = warnings,
-                    PullRequestUrl = pullRequestUrl,
-                    DevNote = devNote,
-                    Overrides = overrides,
-                    Anchor = anchor
-                };
+                yield return new WikiModEntry(
+                    id: ids,
+                    name: names,
+                    author: authors,
+                    nexusId: nexusID,
+                    chucklefishId: chucklefishID,
+                    curseForgeId: curseForgeID,
+                    curseForgeKey: curseForgeKey,
+                    modDropId: modDropID,
+                    githubRepo: githubRepo,
+                    customSourceUrl: customSourceUrl,
+                    customUrl: customUrl,
+                    contentPackFor: contentPackFor,
+                    compatibility: compatibility,
+                    betaCompatibility: betaCompatibility,
+                    warnings: warnings,
+                    pullRequestUrl: pullRequestUrl,
+                    devNote: devNote,
+                    overrides: overrides,
+                    anchor: anchor
+                );
             }
         }
 
@@ -196,10 +190,10 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
                 {
                     Ids = this.GetAttributeAsCsv(node, "data-id"),
                     ChangeLocalVersions = this.GetAttributeAsChangeDescriptor(node, "data-local-version",
-                        raw => SemanticVersion.TryParse(raw, out ISemanticVersion version) ? version.ToString() : raw
+                        raw => SemanticVersion.TryParse(raw, out ISemanticVersion? version) ? version.ToString() : raw
                     ),
                     ChangeRemoteVersions = this.GetAttributeAsChangeDescriptor(node, "data-remote-version",
-                        raw => SemanticVersion.TryParse(raw, out ISemanticVersion version) ? version.ToString() : raw
+                        raw => SemanticVersion.TryParse(raw, out ISemanticVersion? version) ? version.ToString() : raw
                     ),
 
                     ChangeUpdateKeys = this.GetAttributeAsChangeDescriptor(node, "data-update-keys",
@@ -212,7 +206,7 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
         /// <summary>Get an attribute value.</summary>
         /// <param name="element">The element whose attributes to read.</param>
         /// <param name="name">The attribute name.</param>
-        private string GetAttribute(HtmlNode element, string name)
+        private string? GetAttribute(HtmlNode element, string name)
         {
             string value = element.GetAttributeValue(name, null);
             if (string.IsNullOrWhiteSpace(value))
@@ -225,9 +219,9 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
         /// <param name="element">The element whose attributes to read.</param>
         /// <param name="name">The attribute name.</param>
         /// <param name="formatValue">Format an raw entry value when applying changes.</param>
-        private ChangeDescriptor GetAttributeAsChangeDescriptor(HtmlNode element, string name, Func<string, string> formatValue)
+        private ChangeDescriptor? GetAttributeAsChangeDescriptor(HtmlNode element, string name, Func<string, string> formatValue)
         {
-            string raw = this.GetAttribute(element, name);
+            string? raw = this.GetAttribute(element, name);
             return raw != null
                 ? ChangeDescriptor.Parse(raw, out _, formatValue)
                 : null;
@@ -238,7 +232,7 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
         /// <param name="name">The attribute name.</param>
         private string[] GetAttributeAsCsv(HtmlNode element, string name)
         {
-            string raw = this.GetAttribute(element, name);
+            string? raw = this.GetAttribute(element, name);
             return !string.IsNullOrWhiteSpace(raw)
                 ? raw.Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries).Select(p => p.Trim()).ToArray()
                 : Array.Empty<string>();
@@ -250,7 +244,7 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
         /// <param name="name">The attribute name.</param>
         private TEnum? GetAttributeAsEnum<TEnum>(HtmlNode element, string name) where TEnum : struct
         {
-            string raw = this.GetAttribute(element, name);
+            string? raw = this.GetAttribute(element, name);
             if (raw == null)
                 return null;
             if (!Enum.TryParse(raw, true, out TEnum value) && Enum.IsDefined(typeof(TEnum), value))
@@ -261,10 +255,10 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
         /// <summary>Get an attribute value and parse it as a semantic version.</summary>
         /// <param name="element">The element whose attributes to read.</param>
         /// <param name="name">The attribute name.</param>
-        private ISemanticVersion GetAttributeAsSemanticVersion(HtmlNode element, string name)
+        private ISemanticVersion? GetAttributeAsSemanticVersion(HtmlNode element, string name)
         {
-            string raw = this.GetAttribute(element, name);
-            return SemanticVersion.TryParse(raw, out ISemanticVersion version)
+            string? raw = this.GetAttribute(element, name);
+            return SemanticVersion.TryParse(raw, out ISemanticVersion? version)
                 ? version
                 : null;
         }
@@ -274,7 +268,7 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
         /// <param name="name">The attribute name.</param>
         private int? GetAttributeAsNullableInt(HtmlNode element, string name)
         {
-            string raw = this.GetAttribute(element, name);
+            string? raw = this.GetAttribute(element, name);
             if (raw != null && int.TryParse(raw, out int value))
                 return value;
             return null;
@@ -283,7 +277,7 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
         /// <summary>Get the text of an element with the given class name.</summary>
         /// <param name="container">The metadata container.</param>
         /// <param name="className">The field name.</param>
-        private string GetInnerHtml(HtmlNode container, string className)
+        private string? GetInnerHtml(HtmlNode container, string className)
         {
             return container.Descendants().FirstOrDefault(p => p.HasClass(className))?.InnerHtml;
         }
@@ -293,8 +287,22 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
         [SuppressMessage("ReSharper", "UnusedAutoPropertyAccessor.Local")]
         private class ResponseModel
         {
+            /*********
+            ** Accessors
+            *********/
             /// <summary>The parse API results.</summary>
-            public ResponseParseModel Parse { get; set; }
+            public ResponseParseModel Parse { get; }
+
+
+            /*********
+            ** Public methods
+            *********/
+            /// <summary>Construct an instance.</summary>
+            /// <param name="parse">The parse API results.</param>
+            public ResponseModel(ResponseParseModel parse)
+            {
+                this.Parse = parse;
+            }
         }
 
         /// <summary>The inner response model for the MediaWiki parse API.</summary>
@@ -303,8 +311,11 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
         [SuppressMessage("ReSharper", "UnusedAutoPropertyAccessor.Local")]
         private class ResponseParseModel
         {
+            /*********
+            ** Accessors
+            *********/
             /// <summary>The parsed text.</summary>
-            public IDictionary<string, string> Text { get; set; }
+            public IDictionary<string, string> Text { get; } = new Dictionary<string, string>();
         }
     }
 }
diff --git a/src/SMAPI.Toolkit/Framework/Clients/Wiki/WikiCompatibilityInfo.cs b/src/SMAPI.Toolkit/Framework/Clients/Wiki/WikiCompatibilityInfo.cs
index 30e76d04..71c90d0c 100644
--- a/src/SMAPI.Toolkit/Framework/Clients/Wiki/WikiCompatibilityInfo.cs
+++ b/src/SMAPI.Toolkit/Framework/Clients/Wiki/WikiCompatibilityInfo.cs
@@ -1,5 +1,3 @@
-#nullable disable
-
 namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
 {
     /// <summary>Compatibility info for a mod.</summary>
@@ -9,18 +7,37 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
         ** Accessors
         *********/
         /// <summary>The compatibility status.</summary>
-        public WikiCompatibilityStatus Status { get; set; }
+        public WikiCompatibilityStatus Status { get; }
 
         /// <summary>The human-readable summary of the compatibility status or workaround, without HTML formatting.</summary>
-        public string Summary { get; set; }
+        public string? Summary { get; }
 
-        /// <summary>The game or SMAPI version which broke this mod (if applicable).</summary>
-        public string BrokeIn { get; set; }
+        /// <summary>The game or SMAPI version which broke this mod, if applicable.</summary>
+        public string? BrokeIn { get; }
 
         /// <summary>The version of the latest unofficial update, if applicable.</summary>
-        public ISemanticVersion UnofficialVersion { get; set; }
+        public ISemanticVersion? UnofficialVersion { get; }
 
         /// <summary>The URL to the latest unofficial update, if applicable.</summary>
-        public string UnofficialUrl { get; set; }
+        public string? UnofficialUrl { get; }
+
+
+        /*********
+        ** Accessors
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="status">The compatibility status.</param>
+        /// <param name="summary">The human-readable summary of the compatibility status or workaround, without HTML formatting.</param>
+        /// <param name="brokeIn">The game or SMAPI version which broke this mod, if applicable.</param>
+        /// <param name="unofficialVersion">The version of the latest unofficial update, if applicable.</param>
+        /// <param name="unofficialUrl">The URL to the latest unofficial update, if applicable.</param>
+        public WikiCompatibilityInfo(WikiCompatibilityStatus status, string? summary, string? brokeIn, ISemanticVersion? unofficialVersion, string? unofficialUrl)
+        {
+            this.Status = status;
+            this.Summary = summary;
+            this.BrokeIn = brokeIn;
+            this.UnofficialVersion = unofficialVersion;
+            this.UnofficialUrl = unofficialUrl;
+        }
     }
 }
diff --git a/src/SMAPI.Toolkit/Framework/Clients/Wiki/WikiCompatibilityStatus.cs b/src/SMAPI.Toolkit/Framework/Clients/Wiki/WikiCompatibilityStatus.cs
index 2c222b71..5cdf489f 100644
--- a/src/SMAPI.Toolkit/Framework/Clients/Wiki/WikiCompatibilityStatus.cs
+++ b/src/SMAPI.Toolkit/Framework/Clients/Wiki/WikiCompatibilityStatus.cs
@@ -1,5 +1,3 @@
-#nullable disable
-
 namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
 {
     /// <summary>The compatibility status for a mod.</summary>
diff --git a/src/SMAPI.Toolkit/Framework/Clients/Wiki/WikiModEntry.cs b/src/SMAPI.Toolkit/Framework/Clients/Wiki/WikiModEntry.cs
index 91943ff9..fc50125f 100644
--- a/src/SMAPI.Toolkit/Framework/Clients/Wiki/WikiModEntry.cs
+++ b/src/SMAPI.Toolkit/Framework/Clients/Wiki/WikiModEntry.cs
@@ -1,4 +1,4 @@
-#nullable disable
+using System.Diagnostics.CodeAnalysis;
 
 namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
 {
@@ -8,64 +8,114 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
         /*********
         ** Accessors
         *********/
-        /// <summary>The mod's unique ID. If the mod has alternate/old IDs, they're listed in latest to newest order.</summary>
-        public string[] ID { get; set; }
+        /// <summary>The mod's unique ID. If the mod has alternate/old IDs, they're listed in latest to oldest order.</summary>
+        public string[] ID { get; }
 
         /// <summary>The mod's display name. If the mod has multiple names, the first one is the most canonical name.</summary>
-        public string[] Name { get; set; }
+        public string[] Name { get; }
 
-        /// <summary>The mod's author name.  If the author has multiple names, the first one is the most canonical name.</summary>
-        public string[] Author { get; set; }
+        /// <summary>The mod's author name. If the author has multiple names, the first one is the most canonical name.</summary>
+        public string[] Author { get; }
 
         /// <summary>The mod ID on Nexus.</summary>
-        public int? NexusID { get; set; }
+        public int? NexusID { get; }
 
         /// <summary>The mod ID in the Chucklefish mod repo.</summary>
-        public int? ChucklefishID { get; set; }
+        public int? ChucklefishID { get; }
 
         /// <summary>The mod ID in the CurseForge mod repo.</summary>
-        public int? CurseForgeID { get; set; }
+        public int? CurseForgeID { get; }
 
         /// <summary>The mod key in the CurseForge mod repo (used in mod page URLs).</summary>
-        public string CurseForgeKey { get; set; }
+        public string? CurseForgeKey { get; }
 
         /// <summary>The mod ID in the ModDrop mod repo.</summary>
-        public int? ModDropID { get; set; }
+        public int? ModDropID { get; }
 
         /// <summary>The GitHub repository in the form 'owner/repo'.</summary>
-        public string GitHubRepo { get; set; }
+        public string? GitHubRepo { get; }
 
         /// <summary>The URL to a non-GitHub source repo.</summary>
-        public string CustomSourceUrl { get; set; }
+        public string? CustomSourceUrl { get; }
 
         /// <summary>The custom mod page URL (if applicable).</summary>
-        public string CustomUrl { get; set; }
+        public string? CustomUrl { get; }
 
         /// <summary>The name of the mod which loads this content pack, if applicable.</summary>
-        public string ContentPackFor { get; set; }
+        public string? ContentPackFor { get; }
 
         /// <summary>The mod's compatibility with the latest stable version of the game.</summary>
-        public WikiCompatibilityInfo Compatibility { get; set; }
+        public WikiCompatibilityInfo Compatibility { get; }
 
         /// <summary>The mod's compatibility with the latest beta version of the game (if any).</summary>
-        public WikiCompatibilityInfo BetaCompatibility { get; set; }
+        public WikiCompatibilityInfo? BetaCompatibility { get; }
 
         /// <summary>Whether a Stardew Valley or SMAPI beta which affects mod compatibility is in progress. If this is true, <see cref="BetaCompatibility"/> should be used for beta versions of SMAPI instead of <see cref="Compatibility"/>.</summary>
+#if NET5_0_OR_GREATER
+        [MemberNotNullWhen(true, nameof(WikiModEntry.BetaCompatibility))]
+#endif
         public bool HasBetaInfo => this.BetaCompatibility != null;
 
         /// <summary>The human-readable warnings for players about this mod.</summary>
-        public string[] Warnings { get; set; }
+        public string[] Warnings { get; }
 
         /// <summary>The URL of the pull request which submits changes for an unofficial update to the author, if any.</summary>
-        public string PullRequestUrl { get; set; }
+        public string? PullRequestUrl { get; }
 
-        /// <summary>Special notes intended for developers who maintain unofficial updates or submit pull requests. </summary>
-        public string DevNote { get; set; }
+        /// <summary>Special notes intended for developers who maintain unofficial updates or submit pull requests.</summary>
+        public string? DevNote { get; }
 
         /// <summary>The data overrides to apply to the mod's manifest or remote mod page data, if any.</summary>
-        public WikiDataOverrideEntry Overrides { get; set; }
+        public WikiDataOverrideEntry? Overrides { get; }
 
         /// <summary>The link anchor for the mod entry in the wiki compatibility list.</summary>
-        public string Anchor { get; set; }
+        public string? Anchor { get; }
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="id">The mod's unique ID. If the mod has alternate/old IDs, they're listed in latest to oldest order.</param>
+        /// <param name="name">The mod's display name. If the mod has multiple names, the first one is the most canonical name.</param>
+        /// <param name="author">The mod's author name. If the author has multiple names, the first one is the most canonical name.</param>
+        /// <param name="nexusId">The mod ID on Nexus.</param>
+        /// <param name="chucklefishId">The mod ID in the Chucklefish mod repo.</param>
+        /// <param name="curseForgeId">The mod ID in the CurseForge mod repo.</param>
+        /// <param name="curseForgeKey">The mod ID in the CurseForge mod repo.</param>
+        /// <param name="modDropId">The mod ID in the ModDrop mod repo.</param>
+        /// <param name="githubRepo">The GitHub repository in the form 'owner/repo'.</param>
+        /// <param name="customSourceUrl">The URL to a non-GitHub source repo.</param>
+        /// <param name="customUrl">The custom mod page URL (if applicable).</param>
+        /// <param name="contentPackFor">The name of the mod which loads this content pack, if applicable.</param>
+        /// <param name="compatibility">The mod's compatibility with the latest stable version of the game.</param>
+        /// <param name="betaCompatibility">The mod's compatibility with the latest beta version of the game (if any).</param>
+        /// <param name="warnings">The human-readable warnings for players about this mod.</param>
+        /// <param name="pullRequestUrl">The URL of the pull request which submits changes for an unofficial update to the author, if any.</param>
+        /// <param name="devNote">Special notes intended for developers who maintain unofficial updates or submit pull requests.</param>
+        /// <param name="overrides">The data overrides to apply to the mod's manifest or remote mod page data, if any.</param>
+        /// <param name="anchor">The link anchor for the mod entry in the wiki compatibility list.</param>
+        public WikiModEntry(string[] id, string[] name, string[] author, int? nexusId, int? chucklefishId, int? curseForgeId, string? curseForgeKey, int? modDropId, string? githubRepo, string? customSourceUrl, string? customUrl, string? contentPackFor, WikiCompatibilityInfo compatibility, WikiCompatibilityInfo? betaCompatibility, string[] warnings, string? pullRequestUrl, string? devNote, WikiDataOverrideEntry? overrides, string? anchor)
+        {
+            this.ID = id;
+            this.Name = name;
+            this.Author = author;
+            this.NexusID = nexusId;
+            this.ChucklefishID = chucklefishId;
+            this.CurseForgeID = curseForgeId;
+            this.CurseForgeKey = curseForgeKey;
+            this.ModDropID = modDropId;
+            this.GitHubRepo = githubRepo;
+            this.CustomSourceUrl = customSourceUrl;
+            this.CustomUrl = customUrl;
+            this.ContentPackFor = contentPackFor;
+            this.Compatibility = compatibility;
+            this.BetaCompatibility = betaCompatibility;
+            this.Warnings = warnings;
+            this.PullRequestUrl = pullRequestUrl;
+            this.DevNote = devNote;
+            this.Overrides = overrides;
+            this.Anchor = anchor;
+        }
     }
 }
diff --git a/src/SMAPI.Toolkit/Framework/Clients/Wiki/WikiModList.cs b/src/SMAPI.Toolkit/Framework/Clients/Wiki/WikiModList.cs
index 1787197a..24548078 100644
--- a/src/SMAPI.Toolkit/Framework/Clients/Wiki/WikiModList.cs
+++ b/src/SMAPI.Toolkit/Framework/Clients/Wiki/WikiModList.cs
@@ -1,5 +1,3 @@
-#nullable disable
-
 namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
 {
     /// <summary>Metadata from the wiki's mod compatibility list.</summary>
@@ -9,12 +7,27 @@ namespace StardewModdingAPI.Toolkit.Framework.Clients.Wiki
         ** Accessors
         *********/
         /// <summary>The stable game version.</summary>
-        public string StableVersion { get; set; }
+        public string? StableVersion { get; }
 
         /// <summary>The beta game version (if any).</summary>
-        public string BetaVersion { get; set; }
+        public string? BetaVersion { get; }
 
         /// <summary>The mods on the wiki.</summary>
-        public WikiModEntry[] Mods { get; set; }
+        public WikiModEntry[] Mods { get; }
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="stableVersion">The stable game version.</param>
+        /// <param name="betaVersion">The beta game version (if any).</param>
+        /// <param name="mods">The mods on the wiki.</param>
+        public WikiModList(string? stableVersion, string? betaVersion, WikiModEntry[] mods)
+        {
+            this.StableVersion = stableVersion;
+            this.BetaVersion = betaVersion;
+            this.Mods = mods;
+        }
     }
 }
diff --git a/src/SMAPI.Toolkit/SemanticVersion.cs b/src/SMAPI.Toolkit/SemanticVersion.cs
index 2cb27e11..3713758f 100644
--- a/src/SMAPI.Toolkit/SemanticVersion.cs
+++ b/src/SMAPI.Toolkit/SemanticVersion.cs
@@ -119,6 +119,9 @@ namespace StardewModdingAPI.Toolkit
         }
 
         /// <inheritdoc />
+#if NET5_0_OR_GREATER
+        [MemberNotNullWhen(true, nameof(SemanticVersion.PrereleaseTag))]
+#endif
         public bool IsPrerelease()
         {
             return !string.IsNullOrWhiteSpace(this.PrereleaseTag);
diff --git a/src/SMAPI.Toolkit/SemanticVersionComparer.cs b/src/SMAPI.Toolkit/SemanticVersionComparer.cs
index 85c974bd..2eca30df 100644
--- a/src/SMAPI.Toolkit/SemanticVersionComparer.cs
+++ b/src/SMAPI.Toolkit/SemanticVersionComparer.cs
@@ -3,7 +3,7 @@ using System.Collections.Generic;
 namespace StardewModdingAPI.Toolkit
 {
     /// <summary>A comparer for semantic versions based on the <see cref="SemanticVersion.CompareTo(ISemanticVersion)"/> field.</summary>
-    public class SemanticVersionComparer : IComparer<ISemanticVersion>
+    public class SemanticVersionComparer : IComparer<ISemanticVersion?>
     {
         /*********
         ** Accessors