java.lang.NullPointerException

Stack trace:
   java/lang/Throwable.<init>()V
   java/lang/Throwable.<init>(Ljava/lang/String;)V
   java/lang/NullPointerException.<init>(Ljava/lang/String;)V
   org/eclipse/ant/internal/core/ant/ProgressBuildListener.countTarget(Lorg/apache/tools/ant/Target;)I
   org/eclipse/ant/internal/core/ant/ProgressBuildListener.computeWork(Lorg/apache/tools/ant/Project;[Lorg/apache/tools/ant/Target;)I
   org/eclipse/ant/internal/core/ant/ProgressBuildListener.<init>(Lorg/apache/tools/ant/Project;Ljava/util/Vector;Lorg/eclipse/core/runtime/IProgressMonitor;)V
   org/eclipse/ant/internal/core/ant/InternalAntRunner.createMonitorBuildListener(Lorg/apache/tools/ant/Project;)V
   org/eclipse/ant/internal/core/ant/InternalAntRunner.run()V
   java/lang/reflect/AccessibleObject.invokeV(Ljava/lang/Object;[Ljava/lang/Object;)V
   java/lang/reflect/Method.invoke(Ljava/lang/Object;[Ljava/lang/Object;)Ljava/lang/Object;
   org/eclipse/ant/core/AntRunner.run(Lorg/eclipse/core/runtime/IProgressMonitor;)V
   org/eclipse/ui/externaltools/internal/core/AntFileRunner.execute(Lorg/eclipse/core/runtime/IProgressMonitor;Lorg/eclipse/ui/externaltools/internal/core/IRunnerContext;)V
   org/eclipse/ui/externaltools/internal/core/DefaultRunnerContext.executeRunner(Lorg/eclipse/core/runtime/IProgressMonitor;)V
   org/eclipse/ui/externaltools/internal/core/DefaultRunnerContext.run(Lorg/eclipse/core/runtime/IProgressMonitor;Lorg/eclipse/swt/widgets/Shell;)V
   org/eclipse/ui/externaltools/internal/ui/AntLaunchWizard$1.run(Lorg/eclipse/core/runtime/IProgressMonitor;)V
   org/eclipse/jface/operation/ModalContext$ModalContextThread.run()V

Build exception: java.lang.NullPointerException