while running jenkins pipeline job it is shwoing job dsl method 'version()' is not found, Follwoing is the code

sh "git config credential.username ${env.GIT_USERNAME}"
sh "git config credential.helper '!echo password=\$GIT_PASSWORD; echo'"
sh "git config user.name 'jenkins' "
sh "git config user.email 'jenkins-gcs@example.com' "
sh "mvn versions:set -DnewVersion=${version()}"
sh "mvn -T 2C clean install"
if (DO_DEPLOY == "true"){
sh "git tag -a ${version()} -m 'Jenkins Build'"
sh "GIT_ASKPASS=true git push origin ${version()}"
if(gitBranch=="jenkins_slave")

else{
echo "stage build branch"+gitBranch
sh "cd gcs-manifest-beanstalk"
sh "mvn deploy"