Below how my Jenkinsfile looks. I am trying to push or do sth when a branch name is the master is. But in this way I am getting null as a branch name. Below is my entire Jenkinsfile
   node () {
        def app
        stage('Clone repository') {
            checkout scm
        }
        stage('Build image') {
            app = docker.build("runtime-development-tools")
            echo "${env.BRANCH_NAME}"
        }
        stage('Push image') {
            if(env.BRANCH_NAME == "master"){
              echo "Hello master"
             // do something
            }
          }
        }
Other links in StackOverflow, unfortunately, did not help me. My Jenkinsfile and other resources are in git repo. I have multi-branch and I want to perform a specific action if it's master branch.