[Schema Inaccuracy] Several fields in `auto_merge` should be nullable

[bigfootjon]

Schema Inaccuracy

Several APIs related to creating/fetching PRs have an auto_merge key which provides information about how auto merge is configured.

Expected

These fields are actually nullable but are not marked as such

Reproduction Steps

https://api.github.com/repos/javaparser/javaparser/pulls/4565

[nickfloyd]

Thanks for submitting an issue! I've routed this internal to the team that owns the endpoint so it can be addressed.