update seems to work. Tests don't work, but the same error was before any changes

Author: zinkko

tmc-plugin/src/fi/helsinki/cs/tmc/actions/UpdateExercisesAction.java

@@ -46,6 +46,9 @@ public void actionPerformed(ActionEvent e) {
     }
 
     public void run() {
+        if (exercisesToUpdate.isEmpty()) {
+            return;
+        }
         try {
             ListenableFuture<List<Exercise>> downloadFuture = core.downloadExercises(exercisesToUpdate,
                     NBTmcSettings.getDefault());