code: def _global_message_func(nodes):
      return {"x": nodes.data["x"]}
  
imports: import io
  import pickle
  import unittest
  import backend
  import dgl
  import dgl.function
  import networkx
  import pytest
  import scipy.sparse
  from dgl.graph_index import create_graph_index
  from dgl.utils import toindex
  from utils import assert_is_identical, assert_is_identical_hetero, check_graph_equal, get_cases, parametrize_idtype
label_desc: Use image node_id 8 for calling a global function with example usage: _global_message_func(nodes) and returns: dict