import unittest
import typing


def report_humanly_readable_difference(a: typing.Any, b: typing.Any) -> typing.Optional[str]:
    """
    Compare strings, return None whrn they match,
    otherwise a humanly readable difference message.
    """
    cls = unittest.TestCase()
    try:
        cls.assertEqual(a, b)
    except AssertionError as ex:
        return str(ex)
    return None