Fixed None path

Author: syrusakbary

graphql/execution/base.py

@@ -46,7 +46,7 @@ class ResolveInfo(object):
                  'schema', 'fragments', 'root_value', 'operation', 'variable_values', 'context', 'path')
 
     def __init__(self, field_name, field_asts, return_type, parent_type,
-                 schema, fragments, root_value, operation, variable_values, context, path):
+                 schema, fragments, root_value, operation, variable_values, context, path=None):
         self.field_name = field_name
         self.field_asts = field_asts
         self.return_type = return_type