@Nullable
 private NameLocationPair addExtLocation() {
   MapExternalResourceDialog dialog = new MapExternalResourceDialog(null, myProject, null, null);
   if (!dialog.showAndGet()) {
     return null;
   }
   setModified(true);
   return new NameLocationPair(dialog.getUri(), dialog.getResourceLocation(), false);
 }
 @Nullable
 private NameLocationPair editExtLocation(Object o) {
   NameLocationPair pair = (NameLocationPair) o;
   MapExternalResourceDialog dialog =
       new MapExternalResourceDialog(pair.getName(), myProject, null, pair.getLocation());
   if (!dialog.showAndGet()) {
     return null;
   }
   setModified(true);
   return new NameLocationPair(dialog.getUri(), dialog.getResourceLocation(), pair.myShared);
 }