code: def Intersect(self, mask1, mask2):
      
      _CheckFieldMaskMessage(mask1)
      _CheckFieldMaskMessage(mask2)
      tree = _FieldMaskTree(mask1)
      intersection = _FieldMaskTree()
      for path in mask2.paths:
        tree.IntersectPath(path, intersection)
      intersection.ToFieldMask(self)
docs: Intersects mask1 and mask2 into this FieldMask.