In case someone is facing the same issue, I managed to solve my problem with the environment variables returning null. You need to use stage in your pipeline and define the deployment on the stage level, like below:

pipelines:
  branches:
    release/master:
      - stage:
          name: Some name for this stage
          deployment: production
          steps:
            - step: *build-pipeline
            - step: *destructive-pre
            - step: *deploy-full-package
            - step: *deploy-env-spec-config
            - step: *destructive-post