@Override
protected Object openDialogBox(Control cellEditorWindow) {
Display display = cellEditorWindow.getDisplay();
SelectSourcesDialog dialog = new SelectSourcesDialog(display.getActiveShell(), this.readingForm);
int dialogResult = dialog.open();
if (dialogResult != Window.CANCEL) {
return this.readingForm.getSourcesString();
} else {
return null;
}