BLOOM - Fix mask creation by default

[younesbelkada]

• fix niche case where the mask is not fed to the forward function

cc @justheuristic

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[sgugger]

Why would this happen? LGTM otherwise.

[justheuristic]

This happens if user decides to run model(input_ids=some_tensor), which originally happened during prototyping (in a notebook).

It is indeed a niche case;
However, the fact that mask is optional can hint other users to the idea that they can keep it None - and it would be more intuitive if having mask=None would be equivalent to passing all ones, like in GPT2Model for example.