When creating a pipeline manually with Empty Variable, Variable is not assigned to pipeline as of 13.6.2

Summary

When manually creating a pipeline on the pipelines page, you can add variables to that pipeline run. In version previous to 13.6.2, variables could be set with a null value. Now, in 13.6.2, variables added with no value assigned appear to no get applied to the pipeline. I have conditions for some jobs that simply check:

rules:
    - if: '$RUN_ALL_CHECKS != null'

If variables are applied with a value, then they appear in the pipeline.

Steps to reproduce

Manually create a pipeline, add a variable with no value. Variable does not appear applied to pipeline or the jobs.

What is the current bug behavior?

No variable applied

What is the expected correct behavior?

Variable applied with no value

Proposal

I would change the filter function to not filter out variables that do not have a value. Since it seems some users rely on that.