code: def test_as_rgb_Nones():
      with pytest.raises(ValueError):
          mahotas.as_rgb(None, None, None)
  
file_path: mahotas/mahotas/tests/test_stretch.py
imports: from mahotas.stretch import stretch
  import mahotas
  import mahotas
  import pytest
  import numpy
label_desc: Use image node_id 4 for calling a global function with example usage: test_as_rgb_Nones() without return types