DDC-2780 - Fixed issue with IS NULL on join aliases

[lcobucci]

Apply fix from #5680 (with some minor changes)

Fixes #3528

[githoober]

Can this fix be backported to 2.5? We are suffering from this bug, and yet we cannot upgrade to 2.6 due to the current PHP limitation in our organization.

[githoober]

I don't understand why a bug that is introduced in one version of doctrine/orm is never fixed in the same version of the library. It's impossible to use it. For example, L2 was introduced in 2.5, but all bug fixes were applied in 2.6.

[githoober]

#7293

[Ocramius]

I don't understand why a bug that is introduced in one version of doctrine/orm is never fixed in the same version of the library. It's impossible to use it.

We have very limited development resources here, based on free time and volunteering.

We chose to not involve ourselves in long term support plans, as we can't sustain them. Anything that isn't trivial or very important to backport won't be backported to a stable version, but only merged into next minor/major releases depending on whether BC breaks are required or involved.