Jenkinsfile using parallel and when to exceute either the one or the other stage

IfElseDeclarativeParallelJenkinsfile.groovy

#!/usr/bin/env groovy
// see https://jenkins.io/doc/book/pipeline/syntax/

pipeline {
    
    agent any
    
    parameters {
        booleanParam(name: "RELEASE", defaultValue: false)
    }
    
    stages {

        stage("Build") {
            steps {
                sh "./gradlew build"
            }
        }
        
        stage("Publish") {
            parallel {
                stage("Release") {
                    when { expression { params.RELEASE } }
                    steps {
                        sh "./gradlew release"
                    }
                }
                stage('Pre-Release') {
                    when { expression { !params.RELEASE } }
                    steps {
                        sh "./gradlew preRelease"
                    }
                }
            }
        }
    }
}