UniJoin.all() should allow empty list

[fedork]

Hi All.

Not sure if I should just file this as a bug, but let's discuss it here first:

I believe there is no good reason why UniJoin.all() does not accept an empty list as an input. It is a frequent situation when you have arbitrary number of items to process and the number happens to be zero. The reasonable thing to do is to return the empty list.

As of right now it is responsibility of the caller to check that the list is not empty before calling and it is an inconvenience and a bug waiting to happen at runtime if you forget.

Since it is strictly widening the acceptable inputs it should be a safe backwards-compatible change.

Please let me know if you think I am missing some good reason why this can't/shouldn't be changed.

Have a nice day!

[fedork]

I created PR #1930 with how I think this should be implemented

[jponge]

Thanks, I will have a look shortly