title: Gradle Execution failed for task extractReleaseAnnotations > java.lang.NullPointerException
body: <p>I'm trying to set up an Android Library module which depends on two other library modules. We use android.support.annotation framework to add annotations on some of the methods. When I try to build the aar, this is what I get:</p>
  
  <pre><code>:hce_entry:extractReleaseAnnotations FAILED
  Error:Execution failed for task ':hce_entry:extractReleaseAnnotations'.
  &gt; java.lang.NullPointerException (no error message)
  </code></pre>
  
  <p>I tried to get some more information executing gradle build with --stacktrace option, and this is the output:</p>
  
  <pre><code>...
  :hce_entry:extractReleaseAnnotations FAILED
  
  FAILURE: Build failed with an exception.
  
  What went wrong:
  Execution failed for task ':hce_entry:extractReleaseAnnotations'.
  java.lang.NullPointerException (no error message)
  
  Try:
  Run with --info or --debug option to get more log output.
  
  Exception is:
  org.gradle.api.tasks.TaskExecutionException: Execution failed for task ':hce_entry:extractReleaseAnnotations'.
          at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeActions(ExecuteActionsTaskExecuter.java:69)
          at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.execute(ExecuteActionsTaskExecuter.java:46)
          at org.gradle.api.internal.tasks.execution.PostExecutionAnalysisTaskExecuter.execute(PostExecutionAnalysisTaskExecuter.java:35)
          at org.gradle.api.internal.tasks.execution.SkipUpToDateTaskExecuter.execute(SkipUpToDateTaskExecuter.java:64)
          at org.gradle.api.internal.tasks.execution.ValidatingTaskExecuter.execute(ValidatingTaskExecuter.java:58)
          at org.gradle.api.internal.tasks.execution.SkipEmptySourceFilesTaskExecuter.execute(SkipEmptySourceFilesTaskExecuter.java:52)
          at org.gradle.api.internal.tasks.execution.SkipTaskWithNoActionsExecuter.execute(SkipTaskWithNoActionsExecuter.java:52)
          at org.gradle.api.internal.tasks.execution.SkipOnlyIfTaskExecuter.execute(SkipOnlyIfTaskExecuter.java:53)
          at org.gradle.api.internal.tasks.execution.ExecuteAtMostOnceTaskExecuter.execute(ExecuteAtMostOnceTaskExecuter.java:43)
          at org.gradle.execution.taskgraph.DefaultTaskGraphExecuter$EventFiringTaskWorker.execute(DefaultTaskGraphExecuter.java:203)
          at org.gradle.execution.taskgraph.DefaultTaskGraphExecuter$EventFiringTaskWorker.execute(DefaultTaskGraphExecuter.java:185)
          at org.gradle.execution.taskgraph.AbstractTaskPlanExecutor$TaskExecutorWorker.processTask(AbstractTaskPlanExecutor.java:62)
          at org.gradle.execution.taskgraph.AbstractTaskPlanExecutor$TaskExecutorWorker.run(AbstractTaskPlanExecutor.java:50)
          at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor.process(DefaultTaskPlanExecutor.java:25)
          at org.gradle.execution.taskgraph.DefaultTaskGraphExecuter.execute(DefaultTaskGraphExecuter.java:110)
          at org.gradle.execution.SelectedTaskExecutionAction.execute(SelectedTaskExecutionAction.java:37)
          at org.gradle.execution.DefaultBuildExecuter.execute(DefaultBuildExecuter.java:37)
          at org.gradle.execution.DefaultBuildExecuter.access$000(DefaultBuildExecuter.java:23)
          at org.gradle.execution.DefaultBuildExecuter$1.proceed(DefaultBuildExecuter.java:43)
          at org.gradle.execution.DryRunBuildExecutionAction.execute(DryRunBuildExecutionAction.java:32)
          at org.gradle.execution.DefaultBuildExecuter.execute(DefaultBuildExecuter.java:37)
          at org.gradle.execution.DefaultBuildExecuter.execute(DefaultBuildExecuter.java:30)
          at org.gradle.initialization.DefaultGradleLauncher$4.run(DefaultGradleLauncher.java:154)
          at org.gradle.internal.Factories$1.create(Factories.java:22)
          at org.gradle.internal.progress.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:90)
          at org.gradle.internal.progress.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:52)
          at org.gradle.initialization.DefaultGradleLauncher.doBuildStages(DefaultGradleLauncher.java:151)
          at org.gradle.initialization.DefaultGradleLauncher.access$200(DefaultGradleLauncher.java:32)
          at org.gradle.initialization.DefaultGradleLauncher$1.create(DefaultGradleLauncher.java:99)
          at org.gradle.initialization.DefaultGradleLauncher$1.create(DefaultGradleLauncher.java:93)
          at org.gradle.internal.progress.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:90)
          at org.gradle.internal.progress.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:62)
          at org.gradle.initialization.DefaultGradleLauncher.doBuild(DefaultGradleLauncher.java:93)
          at org.gradle.initialization.DefaultGradleLauncher.run(DefaultGradleLauncher.java:82)
          at org.gradle.launcher.exec.InProcessBuildActionExecuter$DefaultBuildController.run(InProcessBuildActionExecuter.java:94)
          at org.gradle.tooling.internal.provider.ExecuteBuildActionRunner.run(ExecuteBuildActionRunner.java:28)
          at org.gradle.launcher.exec.ChainingBuildActionRunner.run(ChainingBuildActionRunner.java:35)
          at org.gradle.launcher.exec.InProcessBuildActionExecuter.execute(InProcessBuildActionExecuter.java:43)
          at org.gradle.launcher.exec.InProcessBuildActionExecuter.execute(InProcessBuildActionExecuter.java:28)
          at org.gradle.launcher.exec.ContinuousBuildActionExecuter.execute(ContinuousBuildActionExecuter.java:77)
          at org.gradle.launcher.exec.ContinuousBuildActionExecuter.execute(ContinuousBuildActionExecuter.java:47)
          at org.gradle.launcher.exec.DaemonUsageSuggestingBuildActionExecuter.execute(DaemonUsageSuggestingBuildActionExecuter.java:51)
          at org.gradle.launcher.exec.DaemonUsageSuggestingBuildActionExecuter.execute(DaemonUsageSuggestingBuildActionExecuter.java:28)
          at org.gradle.launcher.cli.RunBuildAction.run(RunBuildAction.java:43)
          at org.gradle.internal.Actions$RunnableActionAdapter.execute(Actions.java:170)
          at org.gradle.launcher.cli.CommandLineActionFactory$ParseAndBuildAction.execute(CommandLineActionFactory.java:237)
          at org.gradle.launcher.cli.CommandLineActionFactory$ParseAndBuildAction.execute(CommandLineActionFactory.java:210)
          at org.gradle.launcher.cli.JavaRuntimeValidationAction.execute(JavaRuntimeValidationAction.java:35)
          at org.gradle.launcher.cli.JavaRuntimeValidationAction.execute(JavaRuntimeValidationAction.java:24)
          at org.gradle.launcher.cli.CommandLineActionFactory$WithLogging.execute(CommandLineActionFactory.java:206)
          at org.gradle.launcher.cli.CommandLineActionFactory$WithLogging.execute(CommandLineActionFactory.java:169)
          at org.gradle.launcher.cli.ExceptionReportingAction.execute(ExceptionReportingAction.java:33)
          at org.gradle.launcher.cli.ExceptionReportingAction.execute(ExceptionReportingAction.java:22)
          at org.gradle.launcher.Main.doAction(Main.java:33)
          at org.gradle.launcher.bootstrap.EntryPoint.run(EntryPoint.java:45)
          at org.gradle.launcher.bootstrap.ProcessBootstrap.runNoExit(ProcessBootstrap.java:54)
          at org.gradle.launcher.bootstrap.ProcessBootstrap.run(ProcessBootstrap.java:35)
          at org.gradle.launcher.GradleMain.main(GradleMain.java:23)
  Caused by: java.lang.NullPointerException
          at com.android.build.gradle.tasks.annotations.Extractor$AnnotationData.appendExpression(Extractor.java:1603)
          at com.android.build.gradle.tasks.annotations.Extractor$AnnotationData.attributeString(Extractor.java:1592)
          at com.android.build.gradle.tasks.annotations.Extractor$AnnotationData.write(Extractor.java:1545)
          at com.android.build.gradle.tasks.annotations.Extractor$Item.write(Extractor.java:1792)
          at com.android.build.gradle.tasks.annotations.Extractor.writeExternalAnnotations(Extractor.java:769)
          at com.android.build.gradle.tasks.annotations.Extractor.export(Extractor.java:271)
          at com.android.build.gradle.tasks.annotations.Extractor$export$0.call(Unknown Source)
          at com.android.build.gradle.tasks.ExtractAnnotations.compile(ExtractAnnotations.groovy:172)
          at org.gradle.internal.reflect.JavaMethod.invoke(JavaMethod.java:75)
          at org.gradle.api.internal.project.taskfactory.AnnotationProcessingTaskFactory$StandardTaskAction.doExecute(AnnotationProcessingTaskFactory.java:227)
          at org.gradle.api.internal.project.taskfactory.AnnotationProcessingTaskFactory$StandardTaskAction.execute(AnnotationProcessingTaskFactory.java:220)
          at org.gradle.api.internal.project.taskfactory.AnnotationProcessingTaskFactory$StandardTaskAction.execute(AnnotationProcessingTaskFactory.java:209)
          at org.gradle.api.internal.AbstractTask$TaskActionWrapper.execute(AbstractTask.java:585)
          at org.gradle.api.internal.AbstractTask$TaskActionWrapper.execute(AbstractTask.java:568)
          at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeAction(ExecuteActionsTaskExecuter.java:80)
          at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeActions(ExecuteActionsTaskExecuter.java:61)
          ... 57 more
  
  
  BUILD FAILED
  </code></pre>
  
  <p>This is my build.gradle file</p>
  
  <pre><code>apply plugin: 'com.android.library'
  
  android {
      compileSdkVersion 19
      buildToolsVersion '19.1.0'
  
      buildTypes {
          release {
              minifyEnabled false
              proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
          }
          debug {
              debuggable true
              minifyEnabled false
          }
      }
  }
  
  dependencies {
      compile project(':core')
      compile project(':lib')
      compile 'com.android.support:support-v4:23.2.0'
  }
  </code></pre>
  
  <p>Anyone could give me any advice? I'm a bit lost and could not find anything to solve the problem.</p>
  
  <p>Thank you in advance.</p>