AttributeError: 'NoneType' object has no attribute 'point_size'

This error occurs when you are trying to access an attribute or method on an object that is `None`. In other words, the object you are trying to access does not exist, so it has no attributes or methods.

To fix this error, you need to check why the object is `None` and make sure it is initialized properly. You may also need to add error handling to handle cases when the object is `None`.