prevent weird null reference exception in error-handling

docs/release-notes.md

@@ -1,6 +1,10 @@
 ← [README](README.md)
 
 # Release notes
+## Upcoming release
+* For mod authors:
+  * Fixed rare `NullReferenceException` in SMAPI's error-handling.
+
 ## 3.12.2
 Released 05 August 2021 for Stardew Valley 1.5.4 or later.
 

src/SMAPI.Internal/ExceptionExtensions.cs

@@ -13,19 +13,26 @@ namespace StardewModdingAPI.Internal
         /// <param name="exception">The error to summarize.</param>
         public static string GetLogSummary(this Exception exception)
         {
-            switch (exception)
+            try
             {
-                case TypeLoadException ex:
-                    return $"Failed loading type '{ex.TypeName}': {exception}";
+                switch (exception)
+                {
+                    case TypeLoadException ex:
+                        return $"Failed loading type '{ex.TypeName}': {exception}";
 
-                case ReflectionTypeLoadException ex:
-                    string summary = ex.ToString();
-                    foreach (Exception childEx in ex.LoaderExceptions ?? new Exception[0])
-                        summary += $"\n\n{childEx?.GetLogSummary()}";
-                    return summary;
+                    case ReflectionTypeLoadException ex:
+                        string summary = ex.ToString();
+                        foreach (Exception childEx in ex.LoaderExceptions ?? new Exception[0])
+                            summary += $"\n\n{childEx?.GetLogSummary()}";
+                        return summary;
 
-                default:
-                    return exception.ToString();
+                    default:
+                        return exception?.ToString() ?? $"<null exception>\n{Environment.StackTrace}";
+                }
+            }
+            catch (Exception ex)
+            {
+                throw new InvalidOperationException($"Failed handling {exception?.GetType().FullName} (original message: {exception?.Message})", ex);
             }
         }