code: def is_watertight(self):
          
          if self.is_empty:
              return False
          watertight, winding = graph.is_watertight(
              edges=self.edges, edges_sorted=self.edges_sorted)
          self._cache['is_winding_consistent'] = winding
          return watertight
docs: Check if a mesh is watertight by making sure every edge is
          included in two faces.
  
          Returns
          ----------
          is_watertight : bool
            Is mesh watertight or not