GitHub's GraphQL author field is null when the account behind a
comment, review, PR, or issue has been deleted (the ghost user). The
action typed author as non-null and read author.login directly, so a
single comment from a deleted account threw and was swallowed into a
generic 'Failed to fetch PR/issue data', failing the entire run.
Make author nullable on the four affected types and fall back to
'ghost' at each login read. With the type nullable, tsc flags every
dereference, so all sites are covered.
3e807ec379