our turn to be hit by this 7.1 BC break in Symfony:
`ReflectionType::__toString()` now adds a `?` in front of type hints where
`null` is allowed by their default values.
But since `zend_bool` is really an `unsigned char`, we have plenty of room
to store and forward this semantic subtlety (nullable being set through
`?Foo $arg` vs `Foo $arg = null`) so that `ReflectionType::__toString()`
can be accurate again, thus BC.
Thank for you consideration of this patch.