Merge branch 'develop' into stable

5 files changed, 80 insertions, 78 deletions

diff --git a/src/SMAPI.Web/Controllers/IndexController.cs b/src/SMAPI.Web/Controllers/IndexController.cs
index f2f4c342..522d77cd 100644
--- a/src/SMAPI.Web/Controllers/IndexController.cs
+++ b/src/SMAPI.Web/Controllers/IndexController.cs
@@ -57,8 +57,8 @@ namespace StardewModdingAPI.Web.Controllers
         {
             // choose versions
             ReleaseVersion[] versions = await this.GetReleaseVersionsAsync();
-            ReleaseVersion stableVersion = versions.LastOrDefault(version => !version.IsForDevs);
-            ReleaseVersion stableVersionForDevs = versions.LastOrDefault(version => version.IsForDevs);
+            ReleaseVersion? stableVersion = versions.LastOrDefault(version => !version.IsForDevs);
+            ReleaseVersion? stableVersionForDevs = versions.LastOrDefault(version => version.IsForDevs);
 
             // render view
             IndexVersionModel stableVersionModel = stableVersion != null
@@ -89,14 +89,14 @@ namespace StardewModdingAPI.Web.Controllers
                 entry.AbsoluteExpiration = DateTimeOffset.UtcNow.Add(this.CacheTime);
 
                 // get latest stable release
-                GitRelease release = await this.GitHub.GetLatestReleaseAsync(this.RepositoryName, includePrerelease: false);
+                GitRelease? release = await this.GitHub.GetLatestReleaseAsync(this.RepositoryName, includePrerelease: false);
 
                 // strip 'noinclude' blocks from release description
                 if (release != null)
                 {
-                    HtmlDocument doc = new HtmlDocument();
+                    HtmlDocument doc = new();
                     doc.LoadHtml(release.Body);
-                    foreach (HtmlNode node in doc.DocumentNode.SelectNodes("//*[@class='noinclude']")?.ToArray() ?? new HtmlNode[0])
+                    foreach (HtmlNode node in doc.DocumentNode.SelectNodes("//*[@class='noinclude']")?.ToArray() ?? Array.Empty<HtmlNode>())
                         node.Remove();
                     release.Body = doc.DocumentNode.InnerHtml.Trim();
                 }
@@ -111,7 +111,7 @@ namespace StardewModdingAPI.Web.Controllers
 
         /// <summary>Get a parsed list of SMAPI downloads for a release.</summary>
         /// <param name="release">The GitHub release.</param>
-        private IEnumerable<ReleaseVersion> ParseReleaseVersions(GitRelease release)
+        private IEnumerable<ReleaseVersion> ParseReleaseVersions(GitRelease? release)
         {
             if (release?.Assets == null)
                 yield break;
@@ -122,7 +122,7 @@ namespace StardewModdingAPI.Web.Controllers
                     continue;
 
                 Match match = Regex.Match(asset.FileName, @"SMAPI-(?<version>[\d\.]+(?:-.+)?)-installer(?<forDevs>-for-developers)?.zip");
-                if (!match.Success || !SemanticVersion.TryParse(match.Groups["version"].Value, out ISemanticVersion version))
+                if (!match.Success || !SemanticVersion.TryParse(match.Groups["version"].Value, out ISemanticVersion? version))
                     continue;
                 bool isForDevs = match.Groups["forDevs"].Success;
 
diff --git a/src/SMAPI.Web/Controllers/JsonValidatorController.cs b/src/SMAPI.Web/Controllers/JsonValidatorController.cs
index e06c1236..c551a805 100644
--- a/src/SMAPI.Web/Controllers/JsonValidatorController.cs
+++ b/src/SMAPI.Web/Controllers/JsonValidatorController.cs
@@ -64,7 +64,7 @@ namespace StardewModdingAPI.Web.Controllers
         [Route("json/{schemaName}")]
         [Route("json/{schemaName}/{id}")]
         [Route("json/{schemaName}/{id}/{operation}")]
-        public async Task<ViewResult> Index(string schemaName = null, string id = null, string operation = null)
+        public async Task<ViewResult> Index(string? schemaName = null, string? id = null, string? operation = null)
         {
             // parse arguments
             schemaName = this.NormalizeSchemaName(schemaName);
@@ -79,7 +79,7 @@ namespace StardewModdingAPI.Web.Controllers
                 return this.View("Index", result);
 
             // fetch raw JSON
-            StoredFileInfo file = await this.Storage.GetAsync(id, renew);
+            StoredFileInfo file = await this.Storage.GetAsync(id!, renew);
             if (string.IsNullOrWhiteSpace(file.Content))
                 return this.View("Index", result.SetUploadError("The JSON file seems to be empty."));
             result.SetContent(file.Content, expiry: file.Expiry, uploadWarning: file.Warning);
@@ -103,7 +103,7 @@ namespace StardewModdingAPI.Web.Controllers
                 }
                 catch (JsonReaderException ex)
                 {
-                    return this.View("Index", result.AddErrors(new JsonValidatorErrorModel(ex.LineNumber, ex.Path, ex.Message, ErrorType.None)));
+                    return this.View("Index", result.AddErrors(new JsonValidatorErrorModel(ex.LineNumber, ex.Path!, ex.Message, ErrorType.None)));
                 }
 
                 // format JSON
@@ -119,10 +119,10 @@ namespace StardewModdingAPI.Web.Controllers
             // load schema
             JSchema schema;
             {
-                FileInfo schemaFile = this.FindSchemaFile(schemaName);
+                FileInfo? schemaFile = this.FindSchemaFile(schemaName);
                 if (schemaFile == null)
                     return this.View("Index", result.SetParseError($"Invalid schema '{schemaName}'."));
-                schema = JSchema.Parse(System.IO.File.ReadAllText(schemaFile.FullName));
+                schema = JSchema.Parse(await System.IO.File.ReadAllTextAsync(schemaFile.FullName));
             }
 
             // get format doc URL
@@ -142,7 +142,7 @@ namespace StardewModdingAPI.Web.Controllers
         /// <summary>Save raw JSON data.</summary>
         [HttpPost, AllowLargePosts]
         [Route("json")]
-        public async Task<ActionResult> PostAsync(JsonValidatorRequestModel request)
+        public async Task<ActionResult> PostAsync(JsonValidatorRequestModel? request)
         {
             if (request == null)
                 return this.View("Index", this.GetModel(null, null, isEditView: true).SetUploadError("The request seems to be invalid."));
@@ -151,7 +151,7 @@ namespace StardewModdingAPI.Web.Controllers
             string schemaName = this.NormalizeSchemaName(request.SchemaName);
 
             // get raw text
-            string input = request.Content;
+            string? input = request.Content;
             if (string.IsNullOrWhiteSpace(input))
                 return this.View("Index", this.GetModel(null, schemaName, isEditView: true).SetUploadError("The JSON file seems to be empty."));
 
@@ -161,7 +161,7 @@ namespace StardewModdingAPI.Web.Controllers
                 return this.View("Index", this.GetModel(result.ID, schemaName, isEditView: true).SetContent(input, null).SetUploadError(result.UploadError));
 
             // redirect to view
-            return this.Redirect(this.Url.PlainAction("Index", "JsonValidator", new { schemaName = schemaName, id = result.ID }));
+            return this.Redirect(this.Url.PlainAction("Index", "JsonValidator", new { schemaName, id = result.ID })!);
         }
 
 
@@ -172,14 +172,14 @@ namespace StardewModdingAPI.Web.Controllers
         /// <param name="pasteID">The stored file ID.</param>
         /// <param name="schemaName">The schema name with which the JSON was validated.</param>
         /// <param name="isEditView">Whether to show the edit view.</param>
-        private JsonValidatorModel GetModel(string pasteID, string schemaName, bool isEditView)
+        private JsonValidatorModel GetModel(string? pasteID, string? schemaName, bool isEditView)
         {
             return new JsonValidatorModel(pasteID, schemaName, this.SchemaFormats, isEditView);
         }
 
         /// <summary>Get a normalized schema name, or the <see cref="DefaultSchemaID"/> if blank.</summary>
         /// <param name="schemaName">The raw schema name to normalize.</param>
-        private string NormalizeSchemaName(string schemaName)
+        private string NormalizeSchemaName(string? schemaName)
         {
             schemaName = schemaName?.Trim().ToLower();
             return !string.IsNullOrWhiteSpace(schemaName)
@@ -189,7 +189,7 @@ namespace StardewModdingAPI.Web.Controllers
 
         /// <summary>Get the schema file given its unique ID.</summary>
         /// <param name="id">The schema ID.</param>
-        private FileInfo FindSchemaFile(string id)
+        private FileInfo? FindSchemaFile(string? id)
         {
             // normalize ID
             id = id?.Trim().ToLower();
@@ -197,7 +197,7 @@ namespace StardewModdingAPI.Web.Controllers
                 return null;
 
             // get matching file
-            DirectoryInfo schemaDir = new DirectoryInfo(Path.Combine(Directory.GetCurrentDirectory(), "wwwroot", "schemas"));
+            DirectoryInfo schemaDir = new(Path.Combine(Directory.GetCurrentDirectory(), "wwwroot", "schemas"));
             foreach (FileInfo file in schemaDir.EnumerateFiles("*.json"))
             {
                 if (file.Name.Equals($"{id}.json"))
@@ -214,13 +214,13 @@ namespace StardewModdingAPI.Web.Controllers
             // skip through transparent errors
             if (this.IsTransparentError(error))
             {
-                foreach (var model in error.ChildErrors.SelectMany(this.GetErrorModels))
+                foreach (JsonValidatorErrorModel model in error.ChildErrors.SelectMany(this.GetErrorModels))
                     yield return model;
                 yield break;
             }
 
             // get message
-            string message = this.GetOverrideError(error);
+            string? message = this.GetOverrideError(error);
             if (message == null || message == this.TransparentToken)
                 message = this.FlattenErrorMessage(error);
 
@@ -234,7 +234,7 @@ namespace StardewModdingAPI.Web.Controllers
         private string FlattenErrorMessage(ValidationError error, int indent = 0)
         {
             // get override
-            string message = this.GetOverrideError(error);
+            string? message = this.GetOverrideError(error);
             if (message != null && message != this.TransparentToken)
                 return message;
 
@@ -255,7 +255,7 @@ namespace StardewModdingAPI.Web.Controllers
                     break;
 
                 case ErrorType.Required:
-                    message = $"Missing required fields: {string.Join(", ", (List<string>)error.Value)}.";
+                    message = $"Missing required fields: {string.Join(", ", (List<string>)error.Value!)}.";
                     break;
             }
 
@@ -272,7 +272,7 @@ namespace StardewModdingAPI.Web.Controllers
             if (!error.ChildErrors.Any())
                 return false;
 
-            string @override = this.GetOverrideError(error);
+            string? @override = this.GetOverrideError(error);
             return
                 @override == this.TransparentToken
                 || (error.ErrorType == ErrorType.Then && @override == null);
@@ -280,18 +280,18 @@ namespace StardewModdingAPI.Web.Controllers
 
         /// <summary>Get an override error from the JSON schema, if any.</summary>
         /// <param name="error">The schema validation error.</param>
-        private string GetOverrideError(ValidationError error)
+        private string? GetOverrideError(ValidationError error)
         {
-            string GetRawOverrideError()
+            string? GetRawOverrideError()
             {
                 // get override errors
-                IDictionary<string, string> errors = this.GetExtensionField<Dictionary<string, string>>(error.Schema, "@errorMessages");
+                IDictionary<string, string?>? errors = this.GetExtensionField<Dictionary<string, string?>>(error.Schema, "@errorMessages");
                 if (errors == null)
                     return null;
-                errors = new Dictionary<string, string>(errors, StringComparer.OrdinalIgnoreCase);
+                errors = new Dictionary<string, string?>(errors, StringComparer.OrdinalIgnoreCase);
 
                 // match error by type and message
-                foreach ((string target, string errorMessage) in errors)
+                foreach ((string target, string? errorMessage) in errors)
                 {
                     if (!target.Contains(":"))
                         continue;
@@ -302,7 +302,7 @@ namespace StardewModdingAPI.Web.Controllers
                 }
 
                 // match by type
-                return errors.TryGetValue(error.ErrorType.ToString(), out string message)
+                return errors.TryGetValue(error.ErrorType.ToString(), out string? message)
                     ? message?.Trim()
                     : null;
             }
@@ -315,15 +315,12 @@ namespace StardewModdingAPI.Web.Controllers
         /// <typeparam name="T">The field type.</typeparam>
         /// <param name="schema">The schema whose extension fields to search.</param>
         /// <param name="key">The case-insensitive field key.</param>
-        private T GetExtensionField<T>(JSchema schema, string key)
+        private T? GetExtensionField<T>(JSchema schema, string key)
         {
-            if (schema.ExtensionData != null)
+            foreach ((string curKey, JToken value) in schema.ExtensionData)
             {
-                foreach ((string curKey, JToken value) in schema.ExtensionData)
-                {
-                    if (curKey.Equals(key, StringComparison.OrdinalIgnoreCase))
-                        return value.ToObject<T>();
-                }
+                if (curKey.Equals(key, StringComparison.OrdinalIgnoreCase))
+                    return value.ToObject<T>();
             }
 
             return default;
@@ -331,7 +328,7 @@ namespace StardewModdingAPI.Web.Controllers
 
         /// <summary>Format a schema value for display.</summary>
         /// <param name="value">The value to format.</param>
-        private string FormatValue(object value)
+        private string FormatValue(object? value)
         {
             return value switch
             {
diff --git a/src/SMAPI.Web/Controllers/LogParserController.cs b/src/SMAPI.Web/Controllers/LogParserController.cs
index db53d942..33af5a81 100644
--- a/src/SMAPI.Web/Controllers/LogParserController.cs
+++ b/src/SMAPI.Web/Controllers/LogParserController.cs
@@ -45,7 +45,7 @@ namespace StardewModdingAPI.Web.Controllers
         [HttpGet]
         [Route("log")]
         [Route("log/{id}")]
-        public async Task<ActionResult> Index(string id = null, LogViewFormat format = LogViewFormat.Default, bool renew = false)
+        public async Task<ActionResult> Index(string? id = null, LogViewFormat format = LogViewFormat.Default, bool renew = false)
         {
             // fresh page
             if (string.IsNullOrWhiteSpace(id))
@@ -69,7 +69,7 @@ namespace StardewModdingAPI.Web.Controllers
 
                 case LogViewFormat.RawDownload:
                     {
-                        string content = file.Error ?? file.Content;
+                        string content = file.Error ?? file.Content ?? string.Empty;
                         return this.File(Encoding.UTF8.GetBytes(content), "plain/text", $"SMAPI log ({id}).txt");
                     }
 
@@ -87,7 +87,7 @@ namespace StardewModdingAPI.Web.Controllers
         public async Task<ActionResult> PostAsync()
         {
             // get raw log text
-            string input = this.Request.Form["input"].FirstOrDefault();
+            string? input = this.Request.Form["input"].FirstOrDefault();
             if (string.IsNullOrWhiteSpace(input))
                 return this.View("Index", this.GetModel(null, uploadError: "The log file seems to be empty."));
 
@@ -97,7 +97,7 @@ namespace StardewModdingAPI.Web.Controllers
                 return this.View("Index", this.GetModel(null, uploadError: uploadResult.UploadError));
 
             // redirect to view
-            return this.Redirect(this.Url.PlainAction("Index", "LogParser", new { id = uploadResult.ID }));
+            return this.Redirect(this.Url.PlainAction("Index", "LogParser", new { id = uploadResult.ID })!);
         }
 
 
@@ -109,7 +109,7 @@ namespace StardewModdingAPI.Web.Controllers
         /// <param name="expiry">When the uploaded file will no longer be available.</param>
         /// <param name="uploadWarning">A non-blocking warning while uploading the log.</param>
         /// <param name="uploadError">An error which occurred while uploading the log.</param>
-        private LogParserModel GetModel(string pasteID, DateTime? expiry = null, string uploadWarning = null, string uploadError = null)
+        private LogParserModel GetModel(string? pasteID, DateTimeOffset? expiry = null, string? uploadWarning = null, string? uploadError = null)
         {
             Platform? platform = this.DetectClientPlatform();
 
diff --git a/src/SMAPI.Web/Controllers/ModsApiController.cs b/src/SMAPI.Web/Controllers/ModsApiController.cs
index 37d763cc..401bba4f 100644
--- a/src/SMAPI.Web/Controllers/ModsApiController.cs
+++ b/src/SMAPI.Web/Controllers/ModsApiController.cs
@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Linq;
 using System.Threading.Tasks;
@@ -76,10 +77,10 @@ namespace StardewModdingAPI.Web.Controllers
         /// <param name="model">The mod search criteria.</param>
         /// <param name="version">The requested API version.</param>
         [HttpPost]
-        public async Task<IEnumerable<ModEntryModel>> PostAsync([FromBody] ModSearchModel model, [FromRoute] string version)
+        public async Task<IEnumerable<ModEntryModel>> PostAsync([FromBody] ModSearchModel? model, [FromRoute] string version)
         {
             if (model?.Mods == null)
-                return new ModEntryModel[0];
+                return Array.Empty<ModEntryModel>();
 
             ModUpdateCheckConfig config = this.Config.Value;
 
@@ -92,16 +93,16 @@ namespace StardewModdingAPI.Web.Controllers
                     continue;
 
                 // special case: if this is an update check for the official SMAPI repo, check the Nexus mod page for beta versions
-                if (mod.ID == config.SmapiInfo.ID && mod.UpdateKeys?.Any(key => key == config.SmapiInfo.DefaultUpdateKey) == true && mod.InstalledVersion?.IsPrerelease() == true)
-                    mod.UpdateKeys = mod.UpdateKeys.Concat(config.SmapiInfo.AddBetaUpdateKeys).ToArray();
+                if (mod.ID == config.SmapiInfo.ID && mod.UpdateKeys.Any(key => key == config.SmapiInfo.DefaultUpdateKey) && mod.InstalledVersion?.IsPrerelease() == true)
+                    mod.AddUpdateKeys(config.SmapiInfo.AddBetaUpdateKeys);
 
                 // fetch result
                 ModEntryModel result = await this.GetModData(mod, wikiData, model.IncludeExtendedMetadata, model.ApiVersion);
                 if (!model.IncludeExtendedMetadata && (model.ApiVersion == null || mod.InstalledVersion == null))
                 {
-                    var errors = new List<string>(result.Errors);
-                    errors.Add($"This API can't suggest an update because {nameof(model.ApiVersion)} or {nameof(mod.InstalledVersion)} are null, and you didn't specify {nameof(model.IncludeExtendedMetadata)} to get other info. See the SMAPI technical docs for usage.");
-                    result.Errors = errors.ToArray();
+                    result.Errors = result.Errors
+                        .Concat(new[] { $"This API can't suggest an update because {nameof(model.ApiVersion)} or {nameof(mod.InstalledVersion)} are null, and you didn't specify {nameof(model.IncludeExtendedMetadata)} to get other info. See the SMAPI technical docs for usage." })
+                        .ToArray();
                 }
 
                 mods[mod.ID] = result;
@@ -121,26 +122,26 @@ namespace StardewModdingAPI.Web.Controllers
         /// <param name="includeExtendedMetadata">Whether to include extended metadata for each mod.</param>
         /// <param name="apiVersion">The SMAPI version installed by the player.</param>
         /// <returns>Returns the mod data if found, else <c>null</c>.</returns>
-        private async Task<ModEntryModel> GetModData(ModSearchEntryModel search, WikiModEntry[] wikiData, bool includeExtendedMetadata, ISemanticVersion apiVersion)
+        private async Task<ModEntryModel> GetModData(ModSearchEntryModel search, WikiModEntry[] wikiData, bool includeExtendedMetadata, ISemanticVersion? apiVersion)
         {
             // cross-reference data
-            ModDataRecord record = this.ModDatabase.Get(search.ID);
-            WikiModEntry wikiEntry = wikiData.FirstOrDefault(entry => entry.ID.Contains(search.ID.Trim(), StringComparer.OrdinalIgnoreCase));
+            ModDataRecord? record = this.ModDatabase.Get(search.ID);
+            WikiModEntry? wikiEntry = wikiData.FirstOrDefault(entry => entry.ID.Contains(search.ID.Trim(), StringComparer.OrdinalIgnoreCase));
             UpdateKey[] updateKeys = this.GetUpdateKeys(search.UpdateKeys, record, wikiEntry).ToArray();
-            ModOverrideConfig overrides = this.Config.Value.ModOverrides.FirstOrDefault(p => p.ID.Equals(search.ID?.Trim(), StringComparison.OrdinalIgnoreCase));
+            ModOverrideConfig? overrides = this.Config.Value.ModOverrides.FirstOrDefault(p => p.ID.Equals(search.ID.Trim(), StringComparison.OrdinalIgnoreCase));
             bool allowNonStandardVersions = overrides?.AllowNonStandardVersions ?? false;
 
             // SMAPI versions with a '-beta' tag indicate major changes that may need beta mod versions.
             // This doesn't apply to normal prerelease versions which have an '-alpha' tag.
-            bool isSmapiBeta = apiVersion.IsPrerelease() && apiVersion.PrereleaseTag.StartsWith("beta");
+            bool isSmapiBeta = apiVersion != null && apiVersion.IsPrerelease() && apiVersion.PrereleaseTag.StartsWith("beta");
 
             // get latest versions
-            ModEntryModel result = new ModEntryModel { ID = search.ID };
+            ModEntryModel result = new(search.ID);
             IList<string> errors = new List<string>();
-            ModEntryVersionModel main = null;
-            ModEntryVersionModel optional = null;
-            ModEntryVersionModel unofficial = null;
-            ModEntryVersionModel unofficialForBeta = null;
+            ModEntryVersionModel? main = null;
+            ModEntryVersionModel? optional = null;
+            ModEntryVersionModel? unofficial = null;
+            ModEntryVersionModel? unofficialForBeta = null;
             foreach (UpdateKey updateKey in updateKeys)
             {
                 // validate update key
@@ -160,9 +161,9 @@ namespace StardewModdingAPI.Web.Controllers
 
                 // handle versions
                 if (this.IsNewer(data.Version, main?.Version))
-                    main = new ModEntryVersionModel(data.Version, data.Url);
+                    main = new ModEntryVersionModel(data.Version, data.Url!);
                 if (this.IsNewer(data.PreviewVersion, optional?.Version))
-                    optional = new ModEntryVersionModel(data.PreviewVersion, data.Url);
+                    optional = new ModEntryVersionModel(data.PreviewVersion, data.Url!);
             }
 
             // get unofficial version
@@ -170,7 +171,7 @@ namespace StardewModdingAPI.Web.Controllers
                 unofficial = new ModEntryVersionModel(wikiEntry.Compatibility.UnofficialVersion, $"{this.Url.PlainAction("Index", "Mods", absoluteUrl: true)}#{wikiEntry.Anchor}");
 
             // get unofficial version for beta
-            if (wikiEntry?.HasBetaInfo == true)
+            if (wikiEntry is { HasBetaInfo: true })
             {
                 if (wikiEntry.BetaCompatibility.Status == WikiCompatibilityStatus.Unofficial)
                 {
@@ -196,13 +197,13 @@ namespace StardewModdingAPI.Web.Controllers
             if (overrides?.SetUrl != null)
             {
                 if (main != null)
-                    main.Url = overrides.SetUrl;
+                    main = new(main.Version, overrides.SetUrl);
                 if (optional != null)
-                    optional.Url = overrides.SetUrl;
+                    optional = new(optional.Version, overrides.SetUrl);
             }
 
             // get recommended update (if any)
-            ISemanticVersion installedVersion = this.ModSites.GetMappedVersion(search.InstalledVersion?.ToString(), wikiEntry?.Overrides?.ChangeLocalVersions, allowNonStandard: allowNonStandardVersions);
+            ISemanticVersion? installedVersion = this.ModSites.GetMappedVersion(search.InstalledVersion?.ToString(), wikiEntry?.Overrides?.ChangeLocalVersions, allowNonStandard: allowNonStandardVersions);
             if (apiVersion != null && installedVersion != null)
             {
                 // get newer versions
@@ -217,7 +218,7 @@ namespace StardewModdingAPI.Web.Controllers
                     updates.Add(unofficialForBeta);
 
                 // get newest version
-                ModEntryVersionModel newest = null;
+                ModEntryVersionModel? newest = null;
                 foreach (ModEntryVersionModel update in updates)
                 {
                     if (newest == null || update.Version.IsNewerThan(newest.Version))
@@ -243,7 +244,7 @@ namespace StardewModdingAPI.Web.Controllers
         /// <param name="currentVersion">The current semantic version.</param>
         /// <param name="newVersion">The target semantic version.</param>
         /// <param name="useBetaChannel">Whether the user enabled the beta channel and should be offered prerelease updates.</param>
-        private bool IsRecommendedUpdate(ISemanticVersion currentVersion, ISemanticVersion newVersion, bool useBetaChannel)
+        private bool IsRecommendedUpdate(ISemanticVersion currentVersion, [NotNullWhen(true)] ISemanticVersion? newVersion, bool useBetaChannel)
         {
             return
                 newVersion != null
@@ -254,7 +255,7 @@ namespace StardewModdingAPI.Web.Controllers
         /// <summary>Get whether a <paramref name="current"/> version is newer than an <paramref name="other"/> version.</summary>
         /// <param name="current">The current version.</param>
         /// <param name="other">The other version.</param>
-        private bool IsNewer(ISemanticVersion current, ISemanticVersion other)
+        private bool IsNewer([NotNullWhen(true)] ISemanticVersion? current, ISemanticVersion? other)
         {
             return current != null && (other == null || other.IsOlderThan(current));
         }
@@ -263,17 +264,20 @@ namespace StardewModdingAPI.Web.Controllers
         /// <param name="updateKey">The namespaced update key.</param>
         /// <param name="allowNonStandardVersions">Whether to allow non-standard versions.</param>
         /// <param name="mapRemoteVersions">The changes to apply to remote versions for update checks.</param>
-        private async Task<ModInfoModel> GetInfoForUpdateKeyAsync(UpdateKey updateKey, bool allowNonStandardVersions, ChangeDescriptor mapRemoteVersions)
+        private async Task<ModInfoModel> GetInfoForUpdateKeyAsync(UpdateKey updateKey, bool allowNonStandardVersions, ChangeDescriptor? mapRemoteVersions)
         {
+            if (!updateKey.LooksValid)
+                return new ModInfoModel().SetError(RemoteModStatus.DoesNotExist, $"Invalid update key '{updateKey}'.");
+
             // get mod page
             IModPage page;
             {
                 bool isCached =
-                    this.ModCache.TryGetMod(updateKey.Site, updateKey.ID, out Cached<IModPage> cachedMod)
+                    this.ModCache.TryGetMod(updateKey.Site, updateKey.ID, out Cached<IModPage>? cachedMod)
                     && !this.ModCache.IsStale(cachedMod.LastUpdated, cachedMod.Data.Status == RemoteModStatus.TemporaryError ? this.Config.Value.ErrorCacheMinutes : this.Config.Value.SuccessCacheMinutes);
 
                 if (isCached)
-                    page = cachedMod.Data;
+                    page = cachedMod!.Data;
                 else
                 {
                     page = await this.ModSites.GetModPageAsync(updateKey);
@@ -289,7 +293,7 @@ namespace StardewModdingAPI.Web.Controllers
         /// <param name="specifiedKeys">The specified update keys.</param>
         /// <param name="record">The mod's entry in SMAPI's internal database.</param>
         /// <param name="entry">The mod's entry in the wiki list.</param>
-        private IEnumerable<UpdateKey> GetUpdateKeys(string[] specifiedKeys, ModDataRecord record, WikiModEntry entry)
+        private IEnumerable<UpdateKey> GetUpdateKeys(string[]? specifiedKeys, ModDataRecord? record, WikiModEntry? entry)
         {
             // get unique update keys
             List<UpdateKey> updateKeys = this.GetUnfilteredUpdateKeys(specifiedKeys, record, entry)
@@ -308,7 +312,7 @@ namespace StardewModdingAPI.Web.Controllers
             // if the list has both an update key (like "Nexus:2400") and subkey (like "Nexus:2400@subkey") for the same page, the subkey takes priority
             {
                 var removeKeys = new HashSet<UpdateKey>();
-                foreach (var key in updateKeys)
+                foreach (UpdateKey key in updateKeys)
                 {
                     if (key.Subkey != null)
                         removeKeys.Add(new UpdateKey(key.Site, key.ID, null));
@@ -324,7 +328,7 @@ namespace StardewModdingAPI.Web.Controllers
         /// <param name="specifiedKeys">The specified update keys.</param>
         /// <param name="record">The mod's entry in SMAPI's internal database.</param>
         /// <param name="entry">The mod's entry in the wiki list.</param>
-        private IEnumerable<string> GetUnfilteredUpdateKeys(string[] specifiedKeys, ModDataRecord record, WikiModEntry entry)
+        private IEnumerable<string> GetUnfilteredUpdateKeys(string[]? specifiedKeys, ModDataRecord? record, WikiModEntry? entry)
         {
             // specified update keys
             foreach (string key in specifiedKeys ?? Array.Empty<string>())
@@ -335,7 +339,7 @@ namespace StardewModdingAPI.Web.Controllers
 
             // default update key
             {
-                string defaultKey = record?.GetDefaultUpdateKey();
+                string? defaultKey = record?.GetDefaultUpdateKey();
                 if (!string.IsNullOrWhiteSpace(defaultKey))
                     yield return defaultKey;
             }
diff --git a/src/SMAPI.Web/Controllers/ModsController.cs b/src/SMAPI.Web/Controllers/ModsController.cs
index c62ed605..919afa5b 100644
--- a/src/SMAPI.Web/Controllers/ModsController.cs
+++ b/src/SMAPI.Web/Controllers/ModsController.cs
@@ -1,3 +1,4 @@
+using System;
 using System.Linq;
 using System.Text.RegularExpressions;
 using Microsoft.AspNetCore.Mvc;
@@ -52,8 +53,8 @@ namespace StardewModdingAPI.Web.Controllers
         public ModListModel FetchData()
         {
             // fetch cached data
-            if (!this.Cache.TryGetWikiMetadata(out Cached<WikiMetadata> metadata))
-                return new ModListModel();
+            if (!this.Cache.TryGetWikiMetadata(out Cached<WikiMetadata>? metadata))
+                return new ModListModel(null, null, Array.Empty<ModModel>(), lastUpdated: DateTimeOffset.UtcNow, isStale: true);
 
             // build model
             return new ModListModel(