fix(api): don't 500 on invalid PATCH body

PluralKit.API/Errors.cs

@@ -127,6 +127,10 @@ public static class APIErrorHandlerExt
         if (exc is FormatException && exc.Message.Contains("was not recognized as a valid DateTime"))
             return true;
 
+        // this happens if a user sends an empty JSON object for PATCH (or a JSON object with no valid keys)
+        if (exc is InvalidPatchException)
+            return true;
+
         // This may expanded at some point.
         return false;
     }

PluralKit.Core/Database/Utils/QueryPatchWrapper.cs

@@ -14,11 +14,23 @@ internal class QueryPatchWrapper
         return this;
     }
 
-    public Query ToQuery(Query q) => q.AsUpdate(_dict);
+    public Query ToQuery(Query q)
+    {
+        try
+        {
+            return q.AsUpdate(_dict);
+        }
+        catch (InvalidOperationException)
+        {
+            throw new InvalidPatchException();
+        }
+    }
 }
 
 internal static class SqlKataExtensions
 {
     internal static Query ApplyPatch(this Query query, Func<QueryPatchWrapper, QueryPatchWrapper> func)
         => func(new QueryPatchWrapper()).ToQuery(query);
-}
+}
+
+public class InvalidPatchException : Exception {}

docs/content/api/models.md

@@ -7,7 +7,8 @@ permalink: /api/models
 
 A question mark (`?`) next to the *key name* means the key is optional - it may be omitted in API responses. A question mark next to the *key type* means the key is nullable - API responses may return `null` for that key, instead of the specified type.
 
-In PATCH endpoints, all keys are optional. However, providing an object with no keys (or no valid keys) will result in 500 internal server error.
+In PATCH endpoints, all keys are optional. However, you must provide at least one valid key to update; please use a GET request if you want to query the existing information.
+<br>Sending a PATCH request with an empty JSON object, or with a JSON object that contains no valid keys for the target entity, will result in a 400 bad request error.
 
 Privacy objects (`privacy` key in models) contain values "private" or "public". Patching a privacy value to `null` will set to public. If you do not have access to view the privacy object of the member, the value of the `privacy` key will be null, rather than the values of individual privacy keys.
 
@@ -93,8 +94,7 @@ Every PluralKit entity has two IDs: a short (5-character) ID and a longer UUID.
 |---|---|---|
 |timestamp|datetime||
 |id|snowflake|The ID of the message sent by the webhook. Encoded as string for precision reasons.|
-|original| snowflake|The ID of the (now-deleted) message that triggered the proxy. Encoded as string for precision reasons.|
-|sender|snowflake|The user ID of the account that triggered the proxy. Encoded as string for precision reasons.|
+|original| snowflake|The ID of the (now-deleted) message that triggered the proxy. Encoded as string for precision reasons.||sender|snowflake|The user ID of the account that triggered the proxy. Encoded as string for precision reasons.|
 |channel|snowflake|The ID of the channel the message was sent in. Encoded as string for precision reasons.|
 |guild|snowflake|The ID of the server the message was sent in. Encoded as string for precision reasons.|
 |system?|full System object|The system that proxied the message. Null if the member associated with this message was deleted.|