old_contents: # encoding: utf-8
  
  """
  .. codeauthor:: Tsuyoshi Hombashi <gogogo.vm@gmail.com>
  """
  
  from __future__ import absolute_import
  from __future__ import unicode_literals
  
  import dataproperty
  
  from ._error import NullNameError
  
  
  def _validate_null_string(text):
      if dataproperty.is_empty_string(text):
          raise NullNameError("null name")
  
new_contents: # encoding: utf-8
  
  """
  .. codeauthor:: Tsuyoshi Hombashi <gogogo.vm@gmail.com>
  """
  
  from __future__ import absolute_import
  from __future__ import unicode_literals
  
  import dataproperty
  
  from ._error import NullNameError
  
  
  def _validate_null_string(text, error_msg="null name"):
      if dataproperty.is_empty_string(text):
          raise NullNameError(error_msg)
  
subject: Change to modifiable error message