def get_next_step(self):
        """Find the proper step when user clicks the Next button.

        :returns: The step to be switched to.
        :rtype: WizardStep instance or None
        """
        subcategory = self.parent.step_kw_subcategory.selected_subcategory()
        is_raster = is_raster_layer(self.parent.layer)
        has_classifications = get_classifications(subcategory['key'])

        # Vector
        if not is_raster:
            return self.parent.step_kw_field
        # Raster and has classifications
        elif has_classifications:
            return self.parent.step_kw_multi_classifications
        # else go to source
        return self.parent.step_kw_source
Find the proper step when user clicks the Next button.

        :returns: The step to be switched to.
        :rtype: WizardStep instance or None