[JUNIT] fixed NPE in ActivityHandleTest

Found the NPE while watching the build on the CI.

[junit] 27447 [GUI-THREAD] ERROR
de.fu_berlin.inf.dpp.project.internal.ActivityHandler  - failed to
execute activity: EasyMock for class
de.fu_berlin.inf.dpp.activities.business.JupiterActivity
    [junit] java.lang.NullPointerException
    [junit] 	at
de.fu_berlin.inf.dpp.project.internal.ActivityHandlerTest$1.execute(ActivityHandlerTest.java:96)
    [junit] 	at
de.fu_berlin.inf.dpp.project.internal.ActivityHandler$3.run(ActivityHandler.java:323)
    [junit] 	at de.fu_berlin.inf.dpp.util.Utils$3.run(Utils.java:211)
    [junit] 	at
java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
    [junit] 	at
java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
    [junit] 	at java.util.concurrent.FutureTask.run(FutureTask.java:138)
    [junit] 	at
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    [junit] 	at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    [junit] 	at java.lang.Thread.run(Thread.java:662)


Change-Id: I37eaa875a9efc2123abce9d519ea83134eba5c46
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/924
Tested-by: Jenkins CI
Reviewed-by: Patrick Schlott <pschlottk@gmail.com>