NPE in Note#removeAllAngularObjectInParagraph

ERROR [2020-12-01 12:17:37,270] ({qtp369049246-108785} WebApplicationExceptionMapper.java[toResponse]:49) - Error response
java.lang.NullPointerException
        at org.apache.zeppelin.notebook.Note.removeAllAngularObjectInParagraph(Note.java:923)
        at org.apache.zeppelin.notebook.Note.removeParagraph(Note.java:560)
        at org.apache.zeppelin.service.NotebookService.getNextSessionParagraph(NotebookService.java:659)
        at org.apache.zeppelin.rest.NotebookRestApi.nextSessionParagraph(NotebookRestApi.java:678)
        at sun.reflect.GeneratedMethodAccessor24.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory.lambda$static$0(ResourceMethodInvocationHandlerFactory.java:52)
        at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher$1.run(AbstractJavaResourceMethodDispatcher.java:124)
        at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.invoke(AbstractJavaResourceMethodDispatcher.java:167)
        at org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$ResponseOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:176)
        at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:79)