Potential BC break on master (missing var comparison)

[Richtermeister]

The following expression has changed results between v6.0.0 and current master branch:

{{ _missing == null }}

Given no parameters.
v6.0.0 output: True
master output: False

In understand that null does not have a special meaning in pongo, but I imagine these expressions are out in the wild, and flipping the evaluation would be quite unexpected, so wanted to flag this as potential BC break.

I suspect this is the commit that changed the behavior: 2ef5c88

Thank you for your time.