title: Generating QueryDSL classes with maven fails since 3.1.0
body: <p>When generating QueryDSL's Q... classes with the apt-maven-plugin the maven build fails with a <code>NullPointerException</code> in <code>SimpleSerializerConfig</code> - but only for maven versions since 3.1.0.</p>
  
  <p>We already tried debugging into the maven build but that did not lead to any conclusions.</p>
  
  <p>The maven configuration looks like this:</p>
  
  <pre><code>&lt;plugin&gt;
      &lt;groupId&gt;com.mysema.maven&lt;/groupId&gt;
      &lt;artifactId&gt;apt-maven-plugin&lt;/artifactId&gt;
      &lt;version&gt;1.1.1&lt;/version&gt;
      &lt;executions&gt;
          &lt;execution&gt;
              &lt;goals&gt;
                  &lt;goal&gt;process&lt;/goal&gt;
              &lt;/goals&gt;
              &lt;configuration&gt;
                  &lt;outputDirectory&gt;target/generated-sources/java&lt;/outputDirectory&gt;
                  &lt;processor&gt;com.mysema.query.apt.jpa.JPAAnnotationProcessor&lt;/processor&gt;
                  &lt;logOnlyOnError&gt;true&lt;/logOnlyOnError&gt;
              &lt;/configuration&gt;
          &lt;/execution&gt;
      &lt;/executions&gt;
      &lt;dependencies&gt;
          &lt;dependency&gt;
              &lt;groupId&gt;com.mysema.querydsl&lt;/groupId&gt;
              &lt;artifactId&gt;querydsl-apt&lt;/artifactId&gt;
              &lt;version&gt;${querydsl.version}&lt;/version&gt;
          &lt;/dependency&gt;
          &lt;dependency&gt;
              &lt;groupId&gt;com.mysema.querydsl&lt;/groupId&gt;
              &lt;artifactId&gt;querydsl-jpa&lt;/artifactId&gt;
              &lt;classifier&gt;apt&lt;/classifier&gt;
              &lt;version&gt;${querydsl.version}&lt;/version&gt;
          &lt;/dependency&gt;
      &lt;/dependencies&gt;
  &lt;/plugin&gt;
  </code></pre>
  
  <p>with <code>${querydsl.version}</code> being 2.9.0 - using a newer version does not fix the problem.</p>
  
  <p>The exact stacktrace is</p>
  
  <pre><code>java.lang.RuntimeException: java.lang.NullPointerException
      at com.sun.tools.javac.main.Main.compile(Main.java:469)
      at com.sun.tools.javac.api.JavacTaskImpl.call(JavacTaskImpl.java:132)
      at com.mysema.maven.apt.AbstractProcessorMojo.execute(AbstractProcessorMojo.java:314)
      at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:106)
      at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:208)
      at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
      at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
      at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:84)
      at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:59)
      at org.apache.maven.lifecycle.internal.LifecycleStarter.singleThreadedBuild(LifecycleStarter.java:183)
      at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:161)
      at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:318)
      at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:153)
      at org.apache.maven.cli.MavenCli.execute(MavenCli.java:555)
      at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:214)
      at org.apache.maven.cli.MavenCli.main(MavenCli.java:158)
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      at java.lang.reflect.Method.invoke(Method.java:606)
      at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:290)
      at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:230)
      at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:414)
      at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:357)
  Caused by: java.lang.NullPointerException
      at com.mysema.query.codegen.SimpleSerializerConfig.getConfig(SimpleSerializerConfig.java:29)
      at com.mysema.query.apt.DefaultConfiguration.&lt;init&gt;(DefaultConfiguration.java:129)
      at com.mysema.query.apt.jpa.JPAConfiguration.&lt;init&gt;(JPAConfiguration.java:69)
      at com.mysema.query.apt.jpa.JPAAnnotationProcessor.createConfiguration(JPAAnnotationProcessor.java:46)
      at com.mysema.query.apt.AbstractQuerydslProcessor.process(AbstractQuerydslProcessor.java:102)
      at com.sun.tools.javac.processing.JavacProcessingEnvironment.callProcessor(JavacProcessingEnvironment.java:793)
      at com.sun.tools.javac.processing.JavacProcessingEnvironment.discoverAndRunProcs(JavacProcessingEnvironment.java:722)
      at com.sun.tools.javac.processing.JavacProcessingEnvironment.access$1700(JavacProcessingEnvironment.java:97)
      at com.sun.tools.javac.processing.JavacProcessingEnvironment$Round.run(JavacProcessingEnvironment.java:1029)
      at com.sun.tools.javac.processing.JavacProcessingEnvironment.doProcessing(JavacProcessingEnvironment.java:1163)
      at com.sun.tools.javac.main.JavaCompiler.processAnnotations(JavaCompiler.java:1108)
      at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:824)
      at com.sun.tools.javac.main.Main.compile(Main.java:439)
      ... 23 more
  </code></pre>