When using the user endpoint to create a user, you are able to specify an empty password.
curl -X POST http://localhost:8080/nuxeo/api/v1/user \ -H 'Content-Type: application/json' \ -u Administrator:Administrator \ -d '{ "entity-type":"user", "properties":{"username":"testUser", "password":""} }'
Password should probably follow the regex defined in the user password pattern.