Certain fields that were deemed to be mandatory can in fact be `null`, as demonstrated in newly added tests.

Also, this commit fixes translating `XTrimArgs` to the actual argument array in case `MAXLEN` is set to `0`. That is, in fact, a valid value, as demonstrated by the newly added tests and also by inspecting Redis source code [1].

[1] https://github.com/redis/redis/blob/7.2.4/src/t_stream.c#L941

Fixes #45682