Returns the string message for the given ``error_code``.

        Args:
          cls (JLinkWriteErrors): the ``JLinkWriteErrors`` class
          error_code (int): error code to convert

        Returns:
          An error string corresponding to the error code.

        Raises:
          ValueError: if the error code is invalid.

def to_string(cls, error_code):
        """Returns the string message for the given ``error_code``.

        Args:
          cls (JLinkWriteErrors): the ``JLinkWriteErrors`` class
          error_code (int): error code to convert

        Returns:
          An error string corresponding to the error code.

        Raises:
          ValueError: if the error code is invalid.
        """
        if error_code == cls.ZONE_NOT_FOUND_ERROR:
            return 'Zone not found'
        return super(JLinkWriteErrors, cls).to_string(error_code)