more diagnostics for EA-106944 - NPE: ContributorsBasedGotoByModel.getElementName

platform/lang-impl/src/com/intellij/ide/util/gotoByName/ContributorsBasedGotoByModel.java

@@ -254,7 +254,7 @@ public abstract class ContributorsBasedGotoByModel implements ChooseByNameModelE
   @Override
   public String getElementName(Object element) {
     if (!(element instanceof NavigationItem)) {
-      throw new AssertionError(element + " of " + element.getClass());
+      throw new AssertionError((element == null ? "null" : element + " of " + element.getClass()) + " in " + this + " of " + getClass());
     }
     return ((NavigationItem)element).getName();
   }