Update raises ValueError when given an empty dictionary

[kwzrd]

Passing an empty dictionary to RedisCache.update produces a ValueError from inside the aioredis dependency.

This is inconsistent with the behaviour of a Python dictionary:

>>> d = {"A": 1}
>>> d.update({})
>>> d
{'A': 1}

If this is intended, it should be documented, as the update method's docstring can be misleading:

This works exactly like dict.update from a normal dictionary.

[kwzrd]

To clarify, I understand that RedisCache doesn't attempt to provide an identical interface to a dictionary anymore, for example update also doesn't take kwargs or no arguments at all. But this behaviour is clearly observable from the function signature.

In comparison, the empty dict behaviour is not visible from looking at the implementation unless one looks into aioredis. It feels natural to assume that update({}) is safe. Perhaps the update could check for this case and exit early?