(excluding spl_autoload)
spl_object_id() is of the most interest to me,
since I frequently call it in an application.
This includes false/null types caused by wrong argument types and wrong argument
counts.
I can't rule out iterator_to_array returning null in spl_iterator_apply,
so leave MAY_BE_NULL in.
With review comments by nikic:
Co-Authored-By: Nikita Popov <nikita.ppv@googlemail.com>