def StringRotation(s1: str, s2: str) -> bool:
    """Returns whether s2 is a rotation of s1.

    >>> StringRotation("", "")
    True

    >>> StringRotation("a", "")
    False

    >>> StringRotation("", "b")
    False

    >>> StringRotation("a", "a")
    True

    >>> StringRotation("a", "b")
    False

    >>> StringRotation("ab", "ba")
    True

    >>> StringRotation("aba", "bab")
    False

    >>> StringRotation("abc", "acb")
    False

    >>> StringRotation("erbottlewat", "waterbottle")
    True

    >>> StringRotation("kelly", "ellyk")
    True

    >>> StringRotation("erbottlewat", "waterbottle")
    True
    """

    return len(s1) == len(s2) and s2 in (s1 + s1)