Merge branch 'develop' into stable

23 files changed, 395 insertions, 134 deletions

diff --git a/src/SMAPI.Web/Framework/Clients/Chucklefish/ChucklefishClient.cs b/src/SMAPI.Web/Framework/Clients/Chucklefish/ChucklefishClient.cs
index b8b05878..ce0f1122 100644
--- a/src/SMAPI.Web/Framework/Clients/Chucklefish/ChucklefishClient.cs
+++ b/src/SMAPI.Web/Framework/Clients/Chucklefish/ChucklefishClient.cs
@@ -42,7 +42,7 @@ namespace StardewModdingAPI.Web.Framework.Clients.Chucklefish
 
         /// <summary>Get update check info about a mod.</summary>
         /// <param name="id">The mod ID.</param>
-        public async Task<IModPage> GetModData(string id)
+        public async Task<IModPage?> GetModData(string id)
         {
             IModPage page = new GenericModPage(this.SiteKey, id);
 
@@ -51,14 +51,14 @@ namespace StardewModdingAPI.Web.Framework.Clients.Chucklefish
                 return page.SetError(RemoteModStatus.DoesNotExist, $"The value '{id}' isn't a valid Chucklefish mod ID, must be an integer ID.");
 
             // fetch HTML
-            string html;
+            string? html;
             try
             {
                 html = await this.Client
                     .GetAsync(string.Format(this.ModPageUrlFormat, parsedId))
                     .AsString();
             }
-            catch (ApiException ex) when (ex.Status == HttpStatusCode.NotFound || ex.Status == HttpStatusCode.Forbidden)
+            catch (ApiException ex) when (ex.Status is HttpStatusCode.NotFound or HttpStatusCode.Forbidden)
             {
                 return page.SetError(RemoteModStatus.DoesNotExist, "Found no Chucklefish mod with this ID.");
             }
@@ -67,7 +67,7 @@ namespace StardewModdingAPI.Web.Framework.Clients.Chucklefish
 
             // extract mod info
             string url = this.GetModUrl(parsedId);
-            string version = doc.DocumentNode.SelectSingleNode("//h1/span")?.InnerText;
+            string? version = doc.DocumentNode.SelectSingleNode("//h1/span")?.InnerText;
             string name = doc.DocumentNode.SelectSingleNode("//h1").ChildNodes[0].InnerText.Trim();
             if (name.StartsWith("[SMAPI]"))
                 name = name.Substring("[SMAPI]".Length).TrimStart();
@@ -79,7 +79,7 @@ namespace StardewModdingAPI.Web.Framework.Clients.Chucklefish
         /// <summary>Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.</summary>
         public void Dispose()
         {
-            this.Client?.Dispose();
+            this.Client.Dispose();
         }
 
 
@@ -90,7 +90,7 @@ namespace StardewModdingAPI.Web.Framework.Clients.Chucklefish
         /// <param name="id">The mod ID.</param>
         private string GetModUrl(uint id)
         {
-            UriBuilder builder = new UriBuilder(this.Client.BaseClient.BaseAddress);
+            UriBuilder builder = new(this.Client.BaseClient.BaseAddress!);
             builder.Path += string.Format(this.ModPageUrlFormat, id);
             return builder.Uri.ToString();
         }
diff --git a/src/SMAPI.Web/Framework/Clients/CurseForge/CurseForgeClient.cs b/src/SMAPI.Web/Framework/Clients/CurseForge/CurseForgeClient.cs
index d8008721..d351b42d 100644
--- a/src/SMAPI.Web/Framework/Clients/CurseForge/CurseForgeClient.cs
+++ b/src/SMAPI.Web/Framework/Clients/CurseForge/CurseForgeClient.cs
@@ -17,7 +17,7 @@ namespace StardewModdingAPI.Web.Framework.Clients.CurseForge
         private readonly IClient Client;
 
         /// <summary>A regex pattern which matches a version number in a CurseForge mod file name.</summary>
-        private readonly Regex VersionInNamePattern = new Regex(@"^(?:.+? | *)v?(\d+\.\d+(?:\.\d+)?(?:-.+?)?) *(?:\.(?:zip|rar|7z))?$", RegexOptions.Compiled);
+        private readonly Regex VersionInNamePattern = new(@"^(?:.+? | *)v?(\d+\.\d+(?:\.\d+)?(?:-.+?)?) *(?:\.(?:zip|rar|7z))?$", RegexOptions.Compiled);
 
 
         /*********
@@ -40,7 +40,7 @@ namespace StardewModdingAPI.Web.Framework.Clients.CurseForge
 
         /// <summary>Get update check info about a mod.</summary>
         /// <param name="id">The mod ID.</param>
-        public async Task<IModPage> GetModData(string id)
+        public async Task<IModPage?> GetModData(string id)
         {
             IModPage page = new GenericModPage(this.SiteKey, id);
 
@@ -49,9 +49,9 @@ namespace StardewModdingAPI.Web.Framework.Clients.CurseForge
                 return page.SetError(RemoteModStatus.DoesNotExist, $"The value '{id}' isn't a valid CurseForge mod ID, must be an integer ID.");
 
             // get raw data
-            ModModel mod = await this.Client
+            ModModel? mod = await this.Client
                 .GetAsync($"addon/{parsedId}")
-                .As<ModModel>();
+                .As<ModModel?>();
             if (mod == null)
                 return page.SetError(RemoteModStatus.DoesNotExist, "Found no CurseForge mod with this ID.");
 
@@ -71,7 +71,7 @@ namespace StardewModdingAPI.Web.Framework.Clients.CurseForge
         /// <summary>Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.</summary>
         public void Dispose()
         {
-            this.Client?.Dispose();
+            this.Client.Dispose();
         }
 
 
@@ -80,9 +80,9 @@ namespace StardewModdingAPI.Web.Framework.Clients.CurseForge
         *********/
         /// <summary>Get a raw version string for a mod file, if available.</summary>
         /// <param name="file">The file whose version to get.</param>
-        private string GetRawVersion(ModFileModel file)
+        private string? GetRawVersion(ModFileModel file)
         {
-            Match match = this.VersionInNamePattern.Match(file.DisplayName);
+            Match match = this.VersionInNamePattern.Match(file.DisplayName ?? "");
             if (!match.Success)
                 match = this.VersionInNamePattern.Match(file.FileName);
 
diff --git a/src/SMAPI.Web/Framework/Clients/CurseForge/ResponseModels/ModFileModel.cs b/src/SMAPI.Web/Framework/Clients/CurseForge/ResponseModels/ModFileModel.cs
index 9de74847..e9adcf20 100644
--- a/src/SMAPI.Web/Framework/Clients/CurseForge/ResponseModels/ModFileModel.cs
+++ b/src/SMAPI.Web/Framework/Clients/CurseForge/ResponseModels/ModFileModel.cs
@@ -3,10 +3,26 @@ namespace StardewModdingAPI.Web.Framework.Clients.CurseForge.ResponseModels
     /// <summary>Metadata from the CurseForge API about a mod file.</summary>
     public class ModFileModel
     {
+        /*********
+        ** Accessors
+        *********/
         /// <summary>The file name as downloaded.</summary>
-        public string FileName { get; set; }
+        public string FileName { get; }
 
         /// <summary>The file display name.</summary>
-        public string DisplayName { get; set; }
+        public string? DisplayName { get; }
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="fileName">The file name as downloaded.</param>
+        /// <param name="displayName">The file display name.</param>
+        public ModFileModel(string fileName, string? displayName)
+        {
+            this.FileName = fileName;
+            this.DisplayName = displayName;
+        }
     }
 }
diff --git a/src/SMAPI.Web/Framework/Clients/CurseForge/ResponseModels/ModModel.cs b/src/SMAPI.Web/Framework/Clients/CurseForge/ResponseModels/ModModel.cs
index 48cd185b..fd7796f2 100644
--- a/src/SMAPI.Web/Framework/Clients/CurseForge/ResponseModels/ModModel.cs
+++ b/src/SMAPI.Web/Framework/Clients/CurseForge/ResponseModels/ModModel.cs
@@ -3,16 +3,36 @@ namespace StardewModdingAPI.Web.Framework.Clients.CurseForge.ResponseModels
     /// <summary>An mod from the CurseForge API.</summary>
     public class ModModel
     {
+        /*********
+        ** Accessors
+        *********/
         /// <summary>The mod's unique ID on CurseForge.</summary>
-        public int ID { get; set; }
+        public int ID { get; }
 
         /// <summary>The mod name.</summary>
-        public string Name { get; set; }
+        public string Name { get; }
 
         /// <summary>The web URL for the mod page.</summary>
-        public string WebsiteUrl { get; set; }
+        public string WebsiteUrl { get; }
 
         /// <summary>The available file downloads.</summary>
-        public ModFileModel[] LatestFiles { get; set; }
+        public ModFileModel[] LatestFiles { get; }
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="id">The mod's unique ID on CurseForge.</param>
+        /// <param name="name">The mod name.</param>
+        /// <param name="websiteUrl">The web URL for the mod page.</param>
+        /// <param name="latestFiles">The available file downloads.</param>
+        public ModModel(int id, string name, string websiteUrl, ModFileModel[] latestFiles)
+        {
+            this.ID = id;
+            this.Name = name;
+            this.WebsiteUrl = websiteUrl;
+            this.LatestFiles = latestFiles;
+        }
     }
 }
diff --git a/src/SMAPI.Web/Framework/Clients/GenericModDownload.cs b/src/SMAPI.Web/Framework/Clients/GenericModDownload.cs
index f08b471c..548f17c3 100644
--- a/src/SMAPI.Web/Framework/Clients/GenericModDownload.cs
+++ b/src/SMAPI.Web/Framework/Clients/GenericModDownload.cs
@@ -7,26 +7,23 @@ namespace StardewModdingAPI.Web.Framework.Clients
         ** Accessors
         *********/
         /// <summary>The download's display name.</summary>
-        public string Name { get; set; }
+        public string Name { get; }
 
         /// <summary>The download's description.</summary>
-        public string Description { get; set; }
+        public string? Description { get; }
 
         /// <summary>The download's file version.</summary>
-        public string Version { get; set; }
+        public string? Version { get; }
 
 
         /*********
         ** Public methods
         *********/
-        /// <summary>Construct an empty instance.</summary>
-        public GenericModDownload() { }
-
         /// <summary>Construct an instance.</summary>
         /// <param name="name">The download's display name.</param>
         /// <param name="description">The download's description.</param>
         /// <param name="version">The download's file version.</param>
-        public GenericModDownload(string name, string description, string version)
+        public GenericModDownload(string name, string? description, string? version)
         {
             this.Name = name;
             this.Description = description;
diff --git a/src/SMAPI.Web/Framework/Clients/GenericModPage.cs b/src/SMAPI.Web/Framework/Clients/GenericModPage.cs
index 622e6c56..5353c7e1 100644
--- a/src/SMAPI.Web/Framework/Clients/GenericModPage.cs
+++ b/src/SMAPI.Web/Framework/Clients/GenericModPage.cs
@@ -1,4 +1,6 @@
+using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using StardewModdingAPI.Toolkit.Framework.UpdateData;
 
@@ -17,30 +19,31 @@ namespace StardewModdingAPI.Web.Framework.Clients
         public string Id { get; set; }
 
         /// <summary>The mod name.</summary>
-        public string Name { get; set; }
+        public string? Name { get; set; }
 
         /// <summary>The mod's semantic version number.</summary>
-        public string Version { get; set; }
+        public string? Version { get; set; }
 
         /// <summary>The mod's web URL.</summary>
-        public string Url { get; set; }
+        public string? Url { get; set; }
 
         /// <summary>The mod downloads.</summary>
-        public IModDownload[] Downloads { get; set; } = new IModDownload[0];
+        public IModDownload[] Downloads { get; set; } = Array.Empty<IModDownload>();
 
         /// <summary>The mod availability status on the remote site.</summary>
-        public RemoteModStatus Status { get; set; } = RemoteModStatus.Ok;
+        public RemoteModStatus Status { get; set; } = RemoteModStatus.InvalidData;
 
         /// <summary>A user-friendly error which indicates why fetching the mod info failed (if applicable).</summary>
-        public string Error { get; set; }
+        public string? Error { get; set; }
+
+        /// <summary>Whether the mod data is valid.</summary>
+        [MemberNotNullWhen(true, nameof(IModPage.Name), nameof(IModPage.Url))]
+        public bool IsValid => this.Status == RemoteModStatus.Ok;
 
 
         /*********
         ** Public methods
         *********/
-        /// <summary>Construct an empty instance.</summary>
-        public GenericModPage() { }
-
         /// <summary>Construct an instance.</summary>
         /// <param name="site">The mod site containing the mod.</param>
         /// <param name="id">The mod's unique ID within the site.</param>
@@ -55,12 +58,13 @@ namespace StardewModdingAPI.Web.Framework.Clients
         /// <param name="version">The mod's semantic version number.</param>
         /// <param name="url">The mod's web URL.</param>
         /// <param name="downloads">The mod downloads.</param>
-        public IModPage SetInfo(string name, string version, string url, IEnumerable<IModDownload> downloads)
+        public IModPage SetInfo(string name, string? version, string url, IEnumerable<IModDownload> downloads)
         {
             this.Name = name;
             this.Version = version;
             this.Url = url;
             this.Downloads = downloads.ToArray();
+            this.Status = RemoteModStatus.Ok;
 
             return this;
         }
diff --git a/src/SMAPI.Web/Framework/Clients/GitHub/GitAsset.cs b/src/SMAPI.Web/Framework/Clients/GitHub/GitAsset.cs
index 73ce4025..dbce9368 100644
--- a/src/SMAPI.Web/Framework/Clients/GitHub/GitAsset.cs
+++ b/src/SMAPI.Web/Framework/Clients/GitHub/GitAsset.cs
@@ -5,16 +5,34 @@ namespace StardewModdingAPI.Web.Framework.Clients.GitHub
     /// <summary>A GitHub download attached to a release.</summary>
     internal class GitAsset
     {
+        /*********
+        ** Accessors
+        *********/
         /// <summary>The file name.</summary>
         [JsonProperty("name")]
-        public string FileName { get; set; }
+        public string FileName { get; }
 
         /// <summary>The file content type.</summary>
         [JsonProperty("content_type")]
-        public string ContentType { get; set; }
+        public string ContentType { get; }
 
         /// <summary>The download URL.</summary>
         [JsonProperty("browser_download_url")]
-        public string DownloadUrl { get; set; }
+        public string DownloadUrl { get; }
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="fileName">The file name.</param>
+        /// <param name="contentType">The file content type.</param>
+        /// <param name="downloadUrl">The download URL.</param>
+        public GitAsset(string fileName, string contentType, string downloadUrl)
+        {
+            this.FileName = fileName;
+            this.ContentType = contentType;
+            this.DownloadUrl = downloadUrl;
+        }
     }
 }
diff --git a/src/SMAPI.Web/Framework/Clients/GitHub/GitHubClient.cs b/src/SMAPI.Web/Framework/Clients/GitHub/GitHubClient.cs
index 671f077c..785979a5 100644
--- a/src/SMAPI.Web/Framework/Clients/GitHub/GitHubClient.cs
+++ b/src/SMAPI.Web/Framework/Clients/GitHub/GitHubClient.cs
@@ -33,26 +33,26 @@ namespace StardewModdingAPI.Web.Framework.Clients.GitHub
         /// <param name="acceptHeader">The Accept header value expected by the GitHub API.</param>
         /// <param name="username">The username with which to authenticate to the GitHub API.</param>
         /// <param name="password">The password with which to authenticate to the GitHub API.</param>
-        public GitHubClient(string baseUrl, string userAgent, string acceptHeader, string username, string password)
+        public GitHubClient(string baseUrl, string userAgent, string acceptHeader, string? username, string? password)
         {
             this.Client = new FluentClient(baseUrl)
                 .SetUserAgent(userAgent)
                 .AddDefault(req => req.WithHeader("Accept", acceptHeader));
             if (!string.IsNullOrWhiteSpace(username))
-                this.Client = this.Client.SetBasicAuthentication(username, password);
+                this.Client = this.Client.SetBasicAuthentication(username, password!);
         }
 
         /// <summary>Get basic metadata for a GitHub repository, if available.</summary>
         /// <param name="repo">The repository key (like <c>Pathoschild/SMAPI</c>).</param>
         /// <returns>Returns the repository info if it exists, else <c>null</c>.</returns>
-        public async Task<GitRepo> GetRepositoryAsync(string repo)
+        public async Task<GitRepo?> GetRepositoryAsync(string repo)
         {
             this.AssertKeyFormat(repo);
             try
             {
                 return await this.Client
                     .GetAsync($"repos/{repo}")
-                    .As<GitRepo>();
+                    .As<GitRepo?>();
             }
             catch (ApiException ex) when (ex.Status == HttpStatusCode.NotFound)
             {
@@ -64,7 +64,7 @@ namespace StardewModdingAPI.Web.Framework.Clients.GitHub
         /// <param name="repo">The repository key (like <c>Pathoschild/SMAPI</c>).</param>
         /// <param name="includePrerelease">Whether to return a prerelease version if it's latest.</param>
         /// <returns>Returns the release if found, else <c>null</c>.</returns>
-        public async Task<GitRelease> GetLatestReleaseAsync(string repo, bool includePrerelease = false)
+        public async Task<GitRelease?> GetLatestReleaseAsync(string repo, bool includePrerelease = false)
         {
             this.AssertKeyFormat(repo);
             try
@@ -79,7 +79,7 @@ namespace StardewModdingAPI.Web.Framework.Clients.GitHub
 
                 return await this.Client
                     .GetAsync($"repos/{repo}/releases/latest")
-                    .As<GitRelease>();
+                    .As<GitRelease?>();
             }
             catch (ApiException ex) when (ex.Status == HttpStatusCode.NotFound)
             {
@@ -89,7 +89,7 @@ namespace StardewModdingAPI.Web.Framework.Clients.GitHub
 
         /// <summary>Get update check info about a mod.</summary>
         /// <param name="id">The mod ID.</param>
-        public async Task<IModPage> GetModData(string id)
+        public async Task<IModPage?> GetModData(string id)
         {
             IModPage page = new GenericModPage(this.SiteKey, id);
 
@@ -97,15 +97,15 @@ namespace StardewModdingAPI.Web.Framework.Clients.GitHub
                 return page.SetError(RemoteModStatus.DoesNotExist, $"The value '{id}' isn't a valid GitHub mod ID, must be a username and project name like 'Pathoschild/SMAPI'.");
 
             // fetch repo info
-            GitRepo repository = await this.GetRepositoryAsync(id);
+            GitRepo? repository = await this.GetRepositoryAsync(id);
             if (repository == null)
                 return page.SetError(RemoteModStatus.DoesNotExist, "Found no GitHub repository for this ID.");
             string name = repository.FullName;
             string url = $"{repository.WebUrl}/releases";
 
             // get releases
-            GitRelease latest;
-            GitRelease preview;
+            GitRelease? latest;
+            GitRelease? preview;
             {
                 // get latest release (whether preview or stable)
                 latest = await this.GetLatestReleaseAsync(id, includePrerelease: true);
@@ -116,7 +116,7 @@ namespace StardewModdingAPI.Web.Framework.Clients.GitHub
                 preview = null;
                 if (latest.IsPrerelease)
                 {
-                    GitRelease release = await this.GetLatestReleaseAsync(id, includePrerelease: false);
+                    GitRelease? release = await this.GetLatestReleaseAsync(id, includePrerelease: false);
                     if (release != null)
                     {
                         preview = latest;
@@ -127,8 +127,8 @@ namespace StardewModdingAPI.Web.Framework.Clients.GitHub
 
             // get downloads
             IModDownload[] downloads = new[] { latest, preview }
-                .Where(release => release != null)
-                .Select(release => (IModDownload)new GenericModDownload(release.Name, release.Body, release.Tag))
+                .Where(release => release is not null)
+                .Select(release => (IModDownload)new GenericModDownload(release!.Name, release.Body, release.Tag))
                 .ToArray();
 
             // return info
@@ -138,7 +138,7 @@ namespace StardewModdingAPI.Web.Framework.Clients.GitHub
         /// <summary>Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.</summary>
         public void Dispose()
         {
-            this.Client?.Dispose();
+            this.Client.Dispose();
         }
 
 
diff --git a/src/SMAPI.Web/Framework/Clients/GitHub/GitLicense.cs b/src/SMAPI.Web/Framework/Clients/GitHub/GitLicense.cs
index 736efbe6..24d6c3c5 100644
--- a/src/SMAPI.Web/Framework/Clients/GitHub/GitLicense.cs
+++ b/src/SMAPI.Web/Framework/Clients/GitHub/GitLicense.cs
@@ -5,16 +5,34 @@ namespace StardewModdingAPI.Web.Framework.Clients.GitHub
     /// <summary>The license info for a GitHub project.</summary>
     internal class GitLicense
     {
+        /*********
+        ** Accessors
+        *********/
         /// <summary>The license display name.</summary>
         [JsonProperty("name")]
-        public string Name { get; set; }
+        public string Name { get; }
 
         /// <summary>The SPDX ID for the license.</summary>
         [JsonProperty("spdx_id")]
-        public string SpdxId { get; set; }
+        public string SpdxId { get; }
 
         /// <summary>The URL for the license info.</summary>
         [JsonProperty("url")]
-        public string Url { get; set; }
+        public string Url { get; }
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="name">The license display name.</param>
+        /// <param name="spdxId">The SPDX ID for the license.</param>
+        /// <param name="url">The URL for the license info.</param>
+        public GitLicense(string name, string spdxId, string url)
+        {
+            this.Name = name;
+            this.SpdxId = spdxId;
+            this.Url = url;
+        }
     }
 }
diff --git a/src/SMAPI.Web/Framework/Clients/GitHub/GitRelease.cs b/src/SMAPI.Web/Framework/Clients/GitHub/GitRelease.cs
index d0db5297..9de6f020 100644
--- a/src/SMAPI.Web/Framework/Clients/GitHub/GitRelease.cs
+++ b/src/SMAPI.Web/Framework/Clients/GitHub/GitRelease.cs
@@ -1,3 +1,4 @@
+using System;
 using Newtonsoft.Json;
 
 namespace StardewModdingAPI.Web.Framework.Clients.GitHub
@@ -10,24 +11,45 @@ namespace StardewModdingAPI.Web.Framework.Clients.GitHub
         *********/
         /// <summary>The display name.</summary>
         [JsonProperty("name")]
-        public string Name { get; set; }
+        public string Name { get; }
 
         /// <summary>The semantic version string.</summary>
         [JsonProperty("tag_name")]
-        public string Tag { get; set; }
+        public string Tag { get; }
 
         /// <summary>The Markdown description for the release.</summary>
-        public string Body { get; set; }
+        public string Body { get; internal set; }
 
         /// <summary>Whether this is a draft version.</summary>
         [JsonProperty("draft")]
-        public bool IsDraft { get; set; }
+        public bool IsDraft { get; }
 
         /// <summary>Whether this is a prerelease version.</summary>
         [JsonProperty("prerelease")]
-        public bool IsPrerelease { get; set; }
+        public bool IsPrerelease { get; }
 
         /// <summary>The attached files.</summary>
-        public GitAsset[] Assets { get; set; }
+        public GitAsset[] Assets { get; }
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="name">The display name.</param>
+        /// <param name="tag">The semantic version string.</param>
+        /// <param name="body">The Markdown description for the release.</param>
+        /// <param name="isDraft">Whether this is a draft version.</param>
+        /// <param name="isPrerelease">Whether this is a prerelease version.</param>
+        /// <param name="assets">The attached files.</param>
+        public GitRelease(string name, string tag, string? body, bool isDraft, bool isPrerelease, GitAsset[]? assets)
+        {
+            this.Name = name;
+            this.Tag = tag;
+            this.Body = body ?? string.Empty;
+            this.IsDraft = isDraft;
+            this.IsPrerelease = isPrerelease;
+            this.Assets = assets ?? Array.Empty<GitAsset>();
+        }
     }
 }
diff --git a/src/SMAPI.Web/Framework/Clients/GitHub/GitRepo.cs b/src/SMAPI.Web/Framework/Clients/GitHub/GitRepo.cs
index 7d80576e..879b5e49 100644
--- a/src/SMAPI.Web/Framework/Clients/GitHub/GitRepo.cs
+++ b/src/SMAPI.Web/Framework/Clients/GitHub/GitRepo.cs
@@ -5,16 +5,34 @@ namespace StardewModdingAPI.Web.Framework.Clients.GitHub
     /// <summary>Basic metadata about a GitHub project.</summary>
     internal class GitRepo
     {
+        /*********
+        ** Accessors
+        *********/
         /// <summary>The full repository name, including the owner.</summary>
         [JsonProperty("full_name")]
-        public string FullName { get; set; }
+        public string FullName { get; }
 
         /// <summary>The URL to the repository web page, if any.</summary>
         [JsonProperty("html_url")]
-        public string WebUrl { get; set; }
+        public string? WebUrl { get; }
 
         /// <summary>The code license, if any.</summary>
         [JsonProperty("license")]
-        public GitLicense License { get; set; }
+        public GitLicense? License { get; }
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="fullName">The full repository name, including the owner.</param>
+        /// <param name="webUrl">The URL to the repository web page, if any.</param>
+        /// <param name="license">The code license, if any.</param>
+        public GitRepo(string fullName, string? webUrl, GitLicense? license)
+        {
+            this.FullName = fullName;
+            this.WebUrl = webUrl;
+            this.License = license;
+        }
     }
 }
diff --git a/src/SMAPI.Web/Framework/Clients/GitHub/IGitHubClient.cs b/src/SMAPI.Web/Framework/Clients/GitHub/IGitHubClient.cs
index 0d6f4643..886e32d3 100644
--- a/src/SMAPI.Web/Framework/Clients/GitHub/IGitHubClient.cs
+++ b/src/SMAPI.Web/Framework/Clients/GitHub/IGitHubClient.cs
@@ -12,12 +12,12 @@ namespace StardewModdingAPI.Web.Framework.Clients.GitHub
         /// <summary>Get basic metadata for a GitHub repository, if available.</summary>
         /// <param name="repo">The repository key (like <c>Pathoschild/SMAPI</c>).</param>
         /// <returns>Returns the repository info if it exists, else <c>null</c>.</returns>
-        Task<GitRepo> GetRepositoryAsync(string repo);
+        Task<GitRepo?> GetRepositoryAsync(string repo);
 
         /// <summary>Get the latest release for a GitHub repository.</summary>
         /// <param name="repo">The repository key (like <c>Pathoschild/SMAPI</c>).</param>
         /// <param name="includePrerelease">Whether to return a prerelease version if it's latest.</param>
         /// <returns>Returns the release if found, else <c>null</c>.</returns>
-        Task<GitRelease> GetLatestReleaseAsync(string repo, bool includePrerelease = false);
+        Task<GitRelease?> GetLatestReleaseAsync(string repo, bool includePrerelease = false);
     }
 }
diff --git a/src/SMAPI.Web/Framework/Clients/IModSiteClient.cs b/src/SMAPI.Web/Framework/Clients/IModSiteClient.cs
index 33277711..3697ffae 100644
--- a/src/SMAPI.Web/Framework/Clients/IModSiteClient.cs
+++ b/src/SMAPI.Web/Framework/Clients/IModSiteClient.cs
@@ -18,6 +18,6 @@ namespace StardewModdingAPI.Web.Framework.Clients
         *********/
         /// <summary>Get update check info about a mod.</summary>
         /// <param name="id">The mod ID.</param>
-        Task<IModPage> GetModData(string id);
+        Task<IModPage?> GetModData(string id);
     }
 }
diff --git a/src/SMAPI.Web/Framework/Clients/ModDrop/ModDropClient.cs b/src/SMAPI.Web/Framework/Clients/ModDrop/ModDropClient.cs
index 3a1c5b9d..c60b2c90 100644
--- a/