Allow intermediate node to be None while fallowing flattening

Author: lmazuel

msrest/serialization.py

@@ -1108,6 +1108,11 @@ def rest_key_extractor(attr, attr_desc, data):
             break
         working_key = _decode_attribute_map_key(dict_keys[0])
         working_data = working_data.get(working_key, data)
+        if working_data is None:
+            # If at any point while following flatten JSON path see None, it means
+            # that all properties under are None as well
+            # https://github.com/Azure/msrest-for-python/issues/197
+            return None
         key = '.'.join(dict_keys[1:])
 
     return working_data.get(key)