JAL-4470 fix: check for workers!=null before checking its empty...

diff --git a/src/jalview/gui/PopupMenu.java b/src/jalview/gui/PopupMenu.java
index f4dd579..31e7cbb 100644 (file)
--- a/src/jalview/gui/PopupMenu.java
+++ b/src/jalview/gui/PopupMenu.java
@@ -1779,7 +1779,7 @@ public class PopupMenu extends JPopupMenu implements ColourChangeListener
     List<AlignCalcWorkerI> workers = ap.alignFrame.getViewport()
             .getCalcManager().getRegisteredWorkersOfClass(
                     SecondaryStructureConsensusThread.class);
-    if (!workers.isEmpty())
+    if (workers!=null && !workers.isEmpty())
     {
 
       ap.alignFrame.getViewport().getCalcManager()