If a mojo which is executed in a reactor build, was also build in that build, the digest cannot be computed and a warning and stacktrace is displayed (see JENKINS-5044).
This is unnecessarily verbose and repeated each time the mojo is used. The stacktrace could be left out as the source of the warning is clear.

Example warning:

WARNING: Failed to caculate digest for XyzMojo
09:21:51 java.io.FileNotFoundException: /construction/hudson/workspace/abc/target/classes (Is a directory)
09:21:51 at java.io.FileInputStream.open(Native Method)
09:21:51 at java.io.FileInputStream.<init>(FileInputStream.java:120)
09:21:51 at hudson.maven.ExecutedMojo.<init>(ExecutedMojo.java:99)
09:21:51 at hudson.maven.Maven3Builder$MavenExecutionListener.recordMojoSucceeded(Maven3Builder.java:562)
09:21:51 at hudson.maven.Maven3Builder$MavenExecutionListener.mojoSucceeded(Maven3Builder.java:545)
09:21:51 at org.apache.maven.lifecycle.internal.DefaultExecutionEventCatapult.fire(DefaultExecutionEventCatapult.java:87)
09:21:51 at org.apache.maven.lifecycle.internal.DefaultExecutionEventCatapult.fire(DefaultExecutionEventCatapult.java:42)
09:21:51 at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:228)
09:21:51 at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
09:21:51 at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
09:21:51 at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:84)
09:21:51 at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:59)
09:21:51 at org.apache.maven.lifecycle.internal.LifecycleStarter.singleThreadedBuild(LifecycleStarter.java:183)
09:21:51 at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:161)
09:21:51 at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:320)
09:21:51 at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:156)
09:21:51 at org.jvnet.hudson.maven3.launcher.Maven3Launcher.main(Maven3Launcher.java:79)
09:21:51 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
09:21:51 at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
09:21:51 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
09:21:51 at java.lang.reflect.Method.invoke(Method.java:597)
09:21:51 at org.codehaus.plexus.classworlds.launcher.Launcher.launchStandard(Launcher.java:329)
09:21:51 at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:239)
09:21:51 at org.jvnet.hudson.maven3.agent.Maven3Main.launch(Maven3Main.java:158)
09:21:51 at hudson.maven.Maven3Builder.call(Maven3Builder.java:122)
09:21:51 at hudson.maven.Maven3Builder.call(Maven3Builder.java:74)
09:21:51 at hudson.remoting.UserRequest.perform(UserRequest.java:118)
09:21:51 at hudson.remoting.UserRequest.perform(UserRequest.java:48)
09:21:51 at hudson.remoting.Request$2.run(Request.java:287)
09:21:51 at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
09:21:51 at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
09:21:51 at java.util.concurrent.FutureTask.run(FutureTask.java:138)
09:21:51 at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
09:21:51 at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
09:21:51 at java.lang.Thread.run(Thread.java:662)