The environment variables of git plugin not working in pipeline script.

node {
    checkout changelog: true,
        poll: true,
        scm: [
            $class: 'GitSCM', 
            branches: [[name: "${env.gitlabSourceRepoName}/${env.gitlabSourceBranch}"]],
            doGenerateSubmoduleConfigurations: false, 
            extensions: [
                [$class: 'PruneStaleBranch'],
                [
                    $class: 'PreBuildMerge', options: [
                        fastForwardMode: 'FF', 
                        mergeRemote: 'origin', 
                        mergeStrategy: 'default', 
                        mergeTarget: "${env.gitlabTargetBranch}"
                    ]
                ],
                [$class: 'CleanCheckout']
            ], 
            userRemoteConfigs: [
                [name: 'origin', url: 'git@gitlab.mydomain.com:user/project.git', credentialsId: '8949144f-cca9-4385-8597-ad3c14bbd7ce'],
                [name: "${env.gitlabSourceRepoName}", url: "${env.gitlabSourceRepoURL}", credentialsId: '8949144f-cca9-4385-8597-ad3c14bbd7ce']
            ],
            browser: [$class: 'GitLab', repoUrl: 'http://gitlab.mydomain.com', version: '8.8']
        ]

    echo """
             |GIT_COMMIT: ${GIT_COMMIT}
             |GIT_BRANCH: ${GIT_BRANCH }
             """.stripMargin('|')
}

groovy.lang.MissingPropertyException: No such property: GIT_BRANCH for class: WorkflowScript