''

def remove_value(self, key, value):

    if (key is None):
        raise ValueError('Key    is    None')
    existing = self._dict.get(key)
    if isinstance(existing, set):
        existing.discard(value)
        if (len(existing) == 0):
            del self._dict[key]
    elif (existing == value):
        del self._dict[key]
    else:
        pass
