[PHP-DEV] Needs Feedback - Yield without value in reference generator function does not create notice

[aggelos bellos]

Hello everyone,

In this issue #16761 <https://github.com/php/php-src/issues/16761> it was
verified that in the above code it should throw a notice for both yields:
```

<?phperror_reporting(E_ALL);function &y()
{
  yield null; // warning
  yield; // no warning, agreed to be a bug
}foreach (y() as &$y);

```

I have created this PR <https://github.com/php/php-src/pull/16882>
which adds the "missing" notice but we aren't sure on
how to continue on this.

There are 2 main questions:

   1. Should we continue with adding the missing notice and merge it
also in master?
   2. Should we deprecate / remove the usage of yield without value in
reference generator functions?


- Aggelos Bellos