docs: @SuppressWarnings("unchecked")
      public void setDefaultExceptionHandler(final ExceptionHandler<? super T> exceptionHandler)
      {
          checkNotStarted();
          if (!(this.exceptionHandler instanceof ExceptionHandlerWrapper))
          {
              throw new IllegalStateException("setDefaultExceptionHandler can not be used after handleExceptionsWith");
          }
          ((ExceptionHandlerWrapper<T>)this.exceptionHandler).switchTo(exceptionHandler);
      }