Only clean passed json if it is a dictionary

This addresses an issue where clean dict would fail when some of the application command endpoints passed lists instead of dictionaries.

library/wumpy-rest/wumpy/rest/endpoints/base.py

@@ -276,7 +276,7 @@ async def request(
         """
 
         # Clean up MISSING values
-        if json is not None:
+        if isinstance(json, dict):
             json = self._clean_dict(json)
         if data is not None:
             data = self._clean_dict(data)