Define variable java.version.

Author: uhafner

pom.xml

@@ -47,6 +47,7 @@
   <properties>
     <jenkins.baseline>2.426</jenkins.baseline>
     <jenkins.version>${jenkins.baseline}.3</jenkins.version>
+    <java.version>${maven.compiler.release}</java.version>
     <spotbugs.failOnError>false</spotbugs.failOnError>
     <codingstyle.config.version>4.10.0</codingstyle.config.version>