code: def test_plot_empty_slice(affine_mni):
      """Test that things don't crash when we give a map with
      nothing above threshold. This is only a smoke test.
      """
      img = Nifti1Image(np.zeros((20, 20, 20)), affine_mni)
      plot_img(img, display_mode="y", threshold=1)
      plt.close()
  
file_path: nilearn/nilearn/plotting/tests/test_img_plotting/test_plot_img.py
imports: import matplotlib.pyplot
  import numpy
  import pytest
  from nibabel import Nifti1Image
  from nilearn._utils.niimg import is_binary_niimg
  from nilearn.image import get_data
  from nilearn.plotting import plot_img
label_desc: Use image node_id 4 for calling a global function with example usage: test_plot_empty_slice(affine_mni) without return types