code: public Trigger<? super S> getInsertTrigger() {
          ForInsert<S> forInsert = mForInsert;
          return forInsert.isEmpty() ? null : forInsert;
      }
docs: Returns a consolidated trigger to call for insert operations, or null if
  none. If not null, the consolidated trigger is not a snapshot -- it will
  change as the set of triggers in this manager changes.