Handle null comparisons in ManyToManyPersister

[MatTheCat]

Fixes #5587, #5827 and #7717

The reason for

orm/lib/Doctrine/ORM/Persisters/SqlValueVisitor.php

Lines 34 to 38 in a50a611

	if (($operator === Comparison::EQ || $operator === Comparison::IS) && $value === null) {
	return null;
	} elseif ($operator === Comparison::NEQ && $value === null) {
	return null;
	}

was that BasicEntityPersister replaces null comparisons with IS [NOT] NULL so it does not need the corresponding parameter.

Problem is, ManyToManyPersister has then no longer access to the comparison.

My fix is to remove the condition in SqlValueVisitor and make each persister wary of null comparisons. It feels super weird but tests pass.

[MatTheCat]

Thanks! #5827 and #7717 can be closed; I thought GitHub would do it automatically.

[greg0ire]

I think you have to repeat Fixes every time for that to happen 🙂

[MatTheCat]

Indeed, just read https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword 😅