code: def lowercase(text_string):
      '''
      Converts text_string into lowercase and returns the converted string as type str.
  
      Keyword argument:
  
      - text_string: string instance
  
      Exceptions raised:
  
      - InputError: occurs should a non-string argument be passed
      '''
      if text_string is None or text_string == "":
          return ""
      elif isinstance(text_string, str):
          return text_string.lower()
      else:
          raise InputError("string not passed as argument for text_string"f lowercase(text_string):
      '''
      Converts text_string into lowercase and returns the converted string as type str.
  
      Keyword argument:
  
      - text_string: string instance
  
      Exceptions raised:
  
      - InputError: occurs should a non-string argument be passed
      '''
      if text_string is None or text_string == "":
          return ""
      elif isinstance(text_string, str):
          return text_string.lower()
      else:
          raise InputError("string not passed as argument for text_string")
docs: Converts text_string into lowercase and returns the converted string as type str.
  
      Keyword argument:
  
      - text_string: string instance
  
      Exceptions raised:
  
      - InputError: occurs should a non-string argument be passed