code: def test_initialize_empty_node() -> None:
      dim = 4
      node = VectorNode(dim)
  
      assert isinstance(node.coordinates, np.ndarray)
      for entry in node.next:
          assert entry is node
      for entry in node.prev:
          assert entry is node
  
      assert list(node.area) == [0.0] * dim
      assert list(node.volume) == [0.0] * dim
      assert str(node) == "None"
  
file_path: nevergrad/nevergrad/optimization/multiobjective/test_hypervolume.py
imports: import numpy
  from .hypervolume import VectorNode, VectorLinkedList, HypervolumeIndicator
label_desc: Use image node_id 1 for calling a global function with example usage: test_initialize_empty_node() without return types