[Solved]-Dumpdata with unmanaged models

Just exclude this model using --exclude option. Quote from docs:

The –exclude option may be provided to prevent specific applications
or models (specified as in the form of appname.ModelName) from being
dumped. If you specify a model name to dumpdata, the dumped output
will be restricted to that model, rather than the entire application.
You can also mix application names and model names.

./manage.py dumpdata myApp --exclude=myApp.Backup