선생님 저 댓글 불러오는 거 오류가 뜨는데 오류 내용을 잘 모르겠어요 ㅠ

E/AndroidRuntime: FATAL EXCEPTION: main

    Process: org.cream.creamkgt1, PID: 13403

    com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String to type org.cream.creamkgt1.comment.CommentModel

        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertBean(CustomClassMapper.java:436)

        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToClass(CustomClassMapper.java:232)

        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertToCustomClass(CustomClassMapper.java:80)

        at com.google.firebase.database.DataSnapshot.getValue(DataSnapshot.java:203)

        at org.cream.creamkgt1.board.BoardInsideActivity$getCommentData$postListener$1.onDataChange(BoardInsideActivity.kt:85)

        at com.google.firebase.database.core.ValueEventRegistration.fireEvent(ValueEventRegistration.java:75)

        at com.google.firebase.database.core.view.DataEvent.fire(DataEvent.java:63)

        at com.google.firebase.database.core.view.EventRaiser$1.run(EventRaiser.java:55)

        at android.os.Handler.handleCallback(Handler.java:938)

        at android.os.Handler.dispatchMessage(Handler.java:99)

        at android.os.Looper.loopOnce(Looper.java:201)

        at android.os.Looper.loop(Looper.java:288)

        at android.app.ActivityThread.main(ActivityThread.java:7839)

        at java.lang.reflect.Method.invoke(Native Method)

        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548)

        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)

오류가 저렇게 뜨는데 강의 한 3~4번을 봐도 똑같이 작성했는데 어디가 잘못된걸까요? ㅠ

그리고 게시판 작성을 하면 파이어베이스에 적용이 안되네요... 그 전 강의까지는 등록이 잘 됐는데