FlutterActivityAndFragmentDelegate.getFlutterEngine() 空指针

您好，在Boost2.0把 flutter页面内嵌到 安卓原生fragment的跳转代码是这样的
return FlutterFragment.withNewEngine().url("flt_mt_circle_ListRefreshView").params(params).build();

到了3.0我这样写跳转，报空指针，
return new FlutterBoostFragment.CachedEngineFragmentBuilder().urlParams(params).url("flt_mt_circle_ListRefreshView").build();
报错信息
java.lang.NullPointerException:Attempt to invoke virtual method 'io.flutter.embedding.engine.FlutterEngine io.flutter.embedding.android.FlutterActivityAndFragmentDelegate.getFlutterEngine()' on a null object reference

请问下这里的跳转是哪里不对？应该怎么解决呢

Start by reproducing the null pointer from FlutterBoostFragment.CachedEngineFragmentBuilder and inspect the FlutterActivityAndFragmentDelegate.getFlutterEngine() call named in the stack trace. Compare the Boost 2.0 FlutterFragment construction with the Boost 3.0 fragment path; done means the native Fragment navigation completes without the reported exception.

Written by the indexing model from the issue text.