This error is thrown in django even though it's not even imported anywhere. It's thrown by OpenAPISchemaGenerator as follows:
File "/opt/hostedtoolcache/Python/3.8.13/x64/lib/python3.8/site-packages/drf_yasg/inspectors/field.py", line 406, in <module>
(serializers.NullBooleanField, (openapi.TYPE_BOOLEAN, None)),
AttributeError: module 'rest_framework.serializers' has no attribute 'NullBooleanField'
How do I fix this? link. It doesn't answer the question.