docs: @SuppressWarnings("unchecked")
      public <FRAMETYPE extends WindupVertexFrame> FRAMETYPE findSingletonVariable(Class<FRAMETYPE> type, String name)
      {
          WindupVertexFrame frame = findSingletonVariable(name);
  
          if (type != null && !type.isAssignableFrom(frame.getClass()))
          {
              throw new IllegalTypeArgumentException(name, type, frame.getClass());
          }
  
          return (FRAMETYPE) frame;
      }