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

@@ -374,13 +374,20 @@ def testDecodeInvalidDateTime(self):
                           MyMessage, '{"a_datetime": "invalid"}')
 
     def testDecodeInvalidMessage(self):
-        encoded = """{
-        "a_nested_datetime": {
-          "nested_dt_value": "invalid"
-          }
-        }
-        """
-        self.assertRaises(messages.DecodeError, protojson.decode_message,
+        for encoded in (
+            """{
+            "a_nested_datetime": {
+              "nested_dt_value": "invalid"
+              }
+            }
+            """,
+            """{
+            "a_nested_array": [{
+              "an_integer": 1
+              }]
+            }
+            """):
+            self.assertRaises(messages.DecodeError, protojson.decode_message,
                           MyMessage, encoded)
 
     def testEncodeDateTime(self):