docs: def init_hierarchy(cls, model_admin):
          """Initializes model admin with hierarchy data."""
          hierarchy = getattr(model_admin, 'hierarchy')
  
          if hierarchy:
              if not isinstance(hierarchy, Hierarchy):
                  hierarchy = AdjacencyList()  # For `True` and etc. TODO heuristics maybe.
  
          else:
              hierarchy = NoHierarchy()
  
          model_admin.hierarchy = hierarchy