docs: def set_display_name(self, display_name=None):
          """Sets a display name.
  
          A display name is required and if not set, will be set by the
          provider.
  
          arg:    displayName (string): the new display name
          raise:  InvalidArgument - displayName is invalid
          raise:  NoAccess - metadata.is_readonly() is true
          raise:  NullArgument - displayName is null
          compliance: mandatory - This method must be implemented.
  
          """
          if display_name is None:
              raise NullArgument()
          metadata = Metadata(**settings.METADATA['display_name'])
          if metadata.is_read_only():
              raise NoAccess()
          if self._is_valid_input(display_name, metadata, array=False):
              self._my_map['displayName']['text'] = display_name
          else:
              raise InvalidArgument