added null check for SingleElementPipe (test is still missing)

.settings/edu.umd.cs.findbugs.core.prefs

 #FindBugs User Preferences
-#Tue Apr 28 16:12:41 CEST 2015
+#Thu Apr 30 13:44:10 CEST 2015
 detector_threshold=3
 effort=max
 excludefilter0=.fbExcludeFilterFile|true

src/main/java/teetime/framework/Analysis.java

@@ -128,11 +128,10 @@ public final class Analysis<T extends AnalysisConfiguration> implements Uncaught
 		if (threadableStageJobs.isEmpty()) {
 			throw new IllegalStateException("No stage was added using the addThreadableStage(..) method. Add at least one stage.");
 		}
-		AbstractExceptionListener newListener;
-		Set<Stage> intraStages;
+
 		for (Stage stage : threadableStageJobs) {
-			intraStages = traverseIntraStages(stage);
-			newListener = factory.createInstance();
+			Set<Stage> intraStages = traverseIntraStages(stage);
+			AbstractExceptionListener newListener = factory.createInstance();
 			switch (stage.getTerminationStrategy()) {
 			case BY_SIGNAL: {
 				final RunnableConsumerStage runnable = new RunnableConsumerStage(stage);

src/main/java/teetime/framework/pipe/SingleElementPipe.java

@@ -35,9 +35,12 @@ public final class SingleElementPipe extends AbstractIntraThreadPipe {
 
 	@Override
 	public boolean add(final Object element) {
-		this.element = element;
-		this.reportNewElement();
-		return true;
+		if (null != element) {
+			this.element = element;
+			this.reportNewElement();
+			return true;
+		}
+		return false;
 	}
 
 	@Override