code: def complete_nonnull_value(
      exe_context,  # type: ExecutionContext
      return_type,  # type: GraphQLNonNull
      field_asts,  # type: List[Field]
      info,  # type: ResolveInfo
      path,  # type: List[Union[int, str]]
      result,  # type: Any
  ):
      # type: (...) -> Any
      
      completed = complete_value(
          exe_context, return_type.of_type, field_asts, info, path, result
      )
      if completed is None:
          raise GraphQLError(
              "Cannot return null for non-nullable field {}.{}.".format(
                  info.parent_type, info.field_name
              ),
              field_asts,
              path=path,
          )
  
      return completed
docs: Complete a NonNull value by completing the inner type