Ran phpstan analyze --autoload-file=src/__phutil_library_init__.php -c phpstan.neon -l 1 src/ with phpstan.neon containing:
parameters: excludes_analyse: - */__tests__/*
Are you on PHP7? I think the test failure might be PHP7 specific since we don't see it on the server-side tests (which run on PHP5).
The root issue behind that test failure is T10929.
I believe this has zero use cases, but probably fine to keep.
This doesn't seem like a static analysis error?