CI_PIPELINE_SOURCE doesn't work for Merge Request

I am running the CI Pipeline on Merge Request, however CI_PIPELINE_SOURCE=“push”
What I am expecting is CI_PIPELINE_SOURCE should contain value “merge_request_event”

What am I missing?

Link to docs :- Predefined variables reference | GitLab

found the issue, I was not using rules…
rules:
- if: $CI_PIPELINE_SOURCE == ‘merge_request_event’

CI_PIPELINE_SOURCE was set correctly once I made the pipeline to run on merge requests