@staticmethod
def to_str(value):
    """
        Convert value a string. If value is already a str or None, returne it
        unchanged. If value is a byte, decode it as utf8. Otherwise, fall back
        to the value's repr.
        """
    if value is None:
        return ''
    if isinstance(value, str):
        return value
    elif isinstance(value, bytes):
        return value.decode()
    return repr(value)
