old_contents: from romanesco.format import dict_to_vtkarrays, dict_to_vtkrow
  import vtk
  
  vtk_builder = vtk.vtkMutableDirectedGraph()
  node_fields = input["node_fields"]
  edge_fields = input["edge_fields"]
  dict_to_vtkarrays(input["node_data"], node_fields, vtk_builder.GetVertexData())
  if "children" in input and len(input["children"]) > 0:
      dict_to_vtkarrays(input["children"][0]["edge_data"], edge_fields,
                        vtk_builder.GetEdgeData())
  
  
  def process_node(vtknode, node):
      if "children" in node:
          for n in node["children"]:
              vtkchild = vtk_builder.AddVertex()
              vtkparentedge = vtk_builder.AddGraphEdge(vtknode, vtkchild).GetId()
              dict_to_vtkrow(n["node_data"], vtk_builder.GetVertexData())
              if "edge_data" in n:
                  dict_to_vtkrow(n["edge_data"], vtk_builder.GetEdgeData())
              process_node(vtkchild, n)
  vtk_builder.AddVertex()
  dict_to_vtkrow(input["node_data"], vtk_builder.GetVertexData())
  process_node(0, input)
  output = vtk.vtkTree()
  output.ShallowCopy(vtk_builder)
  
new_contents: from romanesco.format import dict_to_vtkarrays, dict_to_vtkrow
  import vtk
  
  vtk_builder = vtk.vtkMutableDirectedGraph()
  node_fields = input["node_fields"]
  edge_fields = input["edge_fields"]
  dict_to_vtkarrays(input["node_data"], node_fields, vtk_builder.GetVertexData())
  if "children" in input and len(input["children"]) > 0:
      dict_to_vtkarrays(input["children"][0]["edge_data"], edge_fields,
                        vtk_builder.GetEdgeData())
  
  
  def process_node(vtknode, node):
      if "children" in node:
          for n in node["children"]:
              vtkchild = vtk_builder.AddVertex()
              vtkparentedge = vtk_builder.AddGraphEdge(vtknode, vtkchild).GetId()
              dict_to_vtkrow(n["node_data"], vtk_builder.GetVertexData())
              dict_to_vtkrow(n["edge_data"], vtk_builder.GetEdgeData())
              process_node(vtkchild, n)
  vtk_builder.AddVertex()
  dict_to_vtkrow(input["node_data"], vtk_builder.GetVertexData())
  process_node(0, input)
  output = vtk.vtkTree()
  output.ShallowCopy(vtk_builder)
  
subject: Revert "tolerate missing edge data"