Fix #280

Author: thenx

aiohttp_admin/backends/mongo_utils.py

@@ -58,7 +58,7 @@ def apply_trafaret(trafaret, value):
     if isinstance(trafaret, MongoId):
         validate = trafaret.converter
 
-    if isinstance(value, list):
+    if isinstance(value, list) and not isinstance(trafaret, t.List):
         value = [validate(v) for v in value]
     else:
         value = validate(value)