def get_classes(self, field):
        """Gets the classes list for the given field, or None if no classes
        are available.

        Classes are first retrieved from :meth:`classes` if they exist,
        otherwise from :meth:`default_classes`.

        Args:
            field: a field name

        Returns:
            a list of classes, or None
        """
        if field in self.classes:
            return self.classes[field]

        if self.default_classes:
            return self.default_classes

        return None
Gets the classes list for the given field, or None if no classes
        are available.

        Classes are first retrieved from :meth:`classes` if they exist,
        otherwise from :meth:`default_classes`.

        Args:
            field: a field name

        Returns:
            a list of classes, or None
        
fiftyone/core/collections.py