code: def test_empty_model(bin_dense_train_data):
      bin_dense, bin_target = bin_dense_train_data
      clf = CDClassifier(C=1e-5, penalty="l1")
      clf.fit(bin_dense, bin_target)
      assert clf.n_nonzero() == 0
      acc = clf.score(bin_dense, bin_target)
      assert acc == 0.5
  
      clf = CDClassifier(C=1e-5, penalty="l1", debiasing=True)
      clf.fit(bin_dense, bin_target)
      assert clf.n_nonzero() == 0
      acc = clf.score(bin_dense, bin_target)
      assert acc == 0.5
  
imports: import numpy
  import pytest
  from sklearn.datasets import load_digits
  from sklearn.preprocessing import LabelBinarizer
  from lightning.impl.primal_cd import CDClassifier, CDRegressor
  from lightning.impl.tests.utils import check_predict_proba
label_desc: Use image node_id 18 for calling a global function with example usage: test_empty_model(bin_dense_train_data) without return types