Fix unexpected attribute error

Author: vladbarosan

apitools/base/protorpclite/protojson.py

@@ -333,7 +333,10 @@ def decode_field(self, field, value):
 
         elif (isinstance(field, messages.MessageField) and
               issubclass(field.type, messages.Message)):
-            return self.__decode_dictionary(field.type, value)
+            try:
+                return self.__decode_dictionary(field.type, value)
+            except AttributeError as err:
+                raise messages.DecodeError(err)
 
         elif (isinstance(field, messages.FloatField) and
               isinstance(value, (six.integer_types, six.string_types))):

apitools/base/protorpclite/protojson_test.py

@@ -375,9 +375,9 @@ def testDecodeInvalidDateTime(self):
 
     def testDecodeInvalidMessage(self):
         encoded = """{
-        "a_nested_datetime": {
+        "a_nested_datetime": [{
           "nested_dt_value": "invalid"
-          }
+          }]
         }
         """
         self.assertRaises(messages.DecodeError, protojson.decode_message,