Just to clarify ..
count(null) ===0

So if you say this is not a bug as it a non-countable, then you have a new bug, that count(null) should be 1, not 0

Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php

http://php.net/manual/en/function.count.php
> Returns the number of elements in array_or_countable. When the parameter is neither an array nor an object with
> implemented Countable interface, 1 will be returned. There is one exception, if array_or_countable is NULL, 0
> will be returned.

This is likely to not be fixed as although it's clearly not great behaviour, it is how it has been for ages, so fixing it would 'break' lots of 'working' code.

However from PHP 7.2, trying to count a non-countable thing gives a warning notice: https://wiki.php.net/rfc/counting_non_countables

If you have an error handler, that converts all warnings to exceptions, the behaviour is then acceptable.

See also https://3v4l.org/WUgRo for why it works like it does. But as @danack mentioned, this kind of stuff is exactly why count() generates a warning starting with PHP 7.2.

You have 2 exceptions ... why not make it 3?

http://prntscr.com/jui1w0

This is not another exception, as an undefined variable access returns NULL. I've removed the note in http://svn.php.net/viewvc?view=revision&revision=345126, as it is both redundant and nowadays quite unnecessary.