I have the following gitlab-ci.yaml file. And BUILD_NUMBER variable should be passed from upstream job to the downstream one (someproject). With the following configuration this trigger-job will be created and fired each time no matter if BUILD_NUMBER is in context or not:

trigger-job:
 stage: build
 rules:
    - if: '$BUILD_NUMBER != null && $BUILD_NUMBER != ""'
 variables:
  BUILD_NUMBER: ${BUILD_NUMBER}
 trigger:
    project: someproject
    branch: main

If I do remove VARIABLES instruction and just pass pipeline variables with appropriate command – everything works. Why? Does it mean that VARIABLES section runs before RULES one and initialize it to smth other than NULL or “”?

trigger-job:
 stage: build
 rules:
    - if: '$BUILD_NUMBER != null && $BUILD_NUMBER != ""'
 trigger:
    project: someproject
    branch: main
    forward:
      pipeline_variables: true