code: def test_not_null():
      not_null = neurovault.NotNull()
  
      assert not_null == "a"
      assert not_null != ""
      assert str(not_null) == "NotNull()"
  
imports: import hashlib
  import json
  import os
  import re
  import stat
  from urllib import parse
  import numpy
  import pandas
  import pytest
  import requests
  from nilearn._utils.data_gen import generate_fake_fmri
  from nilearn.conftest import _rng
  from nilearn.datasets import neurovault
  from nilearn.image import load_img
label_desc: Use image node_id 16 for calling a global function with example usage: test_not_null() without return types