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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def action_checkbox(self, obj):
 """Renders checkboxes. Disable checkbox for parent item navigation link. """

        if getattr(obj, Hierarchy.UPPER_LEVEL_MODEL_ATTR, False):
            return ''

        return super(HierarchicalModelAdmin, self).action_checkbox(obj)