ConcurrentModificationException in Note#toJson

ERROR [2020-11-30 18:17:23,010] ({qtp667821226-82} NotebookServer.java[onMessage]:461) - Can't handle message: {"op":"GET_NOTE","data":{"id":"2FTA843M1"},"ticket":"anonymous","principal":"anonymous","roles":""}
java.util.ConcurrentModificationException
        at java.util.LinkedList$ListItr.checkForComodification(LinkedList.java:966)
        at java.util.LinkedList$ListItr.next(LinkedList.java:888)
        at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:96)
        at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:61)
        at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:69)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:127)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:245)
        at com.google.gson.internal.bind.ObjectTypeAdapter.write(ObjectTypeAdapter.java:107)
        at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:69)
        at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.write(MapTypeAdapterFactory.java:208)
        at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.write(MapTypeAdapterFactory.java:145)
        at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:69)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:127)
 

ERROR [2020-11-30 18:17:23,018] ({qtp667821226-83} NotebookService.java[runParagraph]:372) - Exception from run
java.util.ConcurrentModificationException
        at java.util.LinkedList$ListItr.checkForComodification(LinkedList.java:966)
        at java.util.LinkedList$ListItr.next(LinkedList.java:888)
        at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:96)
        at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:61)
        at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:69)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:127)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:245)
        at com.google.gson.Gson.toJson(Gson.java:704)
        at com.google.gson.Gson.toJson(Gson.java:683)
        at com.google.gson.Gson.toJson(Gson.java:638)
        at com.google.gson.Gson.toJson(Gson.java:618)
        at org.apache.zeppelin.notebook.Note.toJson(Note.java:1120)
        at org.apache.zeppelin.notebook.repo.VFSNotebookRepo.save(VFSNotebookRepo.java:151)
        at org.apache.zeppelin.notebook.repo.NotebookRepoSync.save(NotebookRepoSync.java:214)
        at org.apache.zeppelin.notebook.NoteManager.saveNote(NoteManager.java:182)