code: def validate_causal_graph(causal_graph: DirectedGraph) -> None:
      for node in causal_graph.nodes:
          validate_node(causal_graph, node)
  
imports: from typing import Any, Callable, Optional, Union
  import networkx
  from dowhy.gcm.causal_mechanisms import ConditionalStochasticModel, FunctionalCausalModel, InvertibleFunctionalCausalModel, StochasticModel
  from dowhy.graph import DirectedGraph, HasNodes, get_ordered_predecessors, is_root_node, validate_acyclic, validate_node_in_graph
label_desc: Use image node_id 4 for calling a global function with example usage: validate_causal_graph(causal_graph) without return types