Update ci/quarkus.Jenkinsfile

Author: beikov

ci/quarkus.Jenkinsfile

@@ -60,7 +60,7 @@ pipeline {
                         sh "echo -e '\\n-XX:MaxMetaspaceSize=1024m'>>./.mvn/jvm.config"
                         withMaven(mavenLocalRepo: env.WORKSPACE + '/.m2repository', publisherStrategy: 'EXPLICIT') {
                             // to account for script-only maven wrapper use in Quarkus:
-                            withEnv(["MAVEN_ARGS=${env.MAVEN_ARGS} ${env.MAVEN_CONFIG}"]) {
+                            withEnv(["MAVEN_ARGS=${env.MAVEN_ARGS?:""} ${env.MAVEN_CONFIG}"]) {
                                 sh "echo \$MAVEN_ARGS"
                                 sh "./mvnw -pl !docs -Dquickly install"
                                 // Need to kill the gradle daemons started during the Maven install run