diff --git a/copulas/multivariate/vine.py b/copulas/multivariate/vine.py
index 27dff9dc..5c801af4 100644
--- a/copulas/multivariate/vine.py
+++ b/copulas/multivariate/vine.py
@@ -248,8 +248,6 @@ def train_vine(self, tree_type):
 
     def get_likelihood(self, uni_matrix):
         """Compute likelihood of the vine."""
-        # TODO: explain what this is supposed to do and make it work
-        # TODO: Alternatively, remove it.
         num_tree = len(self.trees)
         values = np.empty([1, num_tree])
 
diff --git a/setup.py b/setup.py
index 19a6d75a..a72fdd7f 100644
--- a/setup.py
+++ b/setup.py
@@ -40,6 +40,7 @@
     'flake8-debugger>=4.0.0,<4.1',
     'flake8-mock>=0.3,<0.4',
     'flake8-mutable>=1.2.0,<1.3',
+    'flake8-fixme>=1.1.1,<1.2',
     'pep8-naming>=0.12.1,<0.13',
     'dlint>=0.11.0,<0.12',
     'flake8-docstrings>=1.5.0,<2',
diff --git a/tests/unit/multivariate/test_gaussian.py b/tests/unit/multivariate/test_gaussian.py
index 6f9073d4..d24fcc03 100644
--- a/tests/unit/multivariate/test_gaussian.py
+++ b/tests/unit/multivariate/test_gaussian.py
@@ -458,7 +458,7 @@ def test_sample_constant_column(self):
 
         # Check
         assert result.shape == (5, 2)
-        results = result[~result.is()].all()
+        results = result[~result.isna()].all()
         assert results.all()
         assert result.loc[:, 0].equals(pd.Series([1.0, 1.0, 1.0, 1.0, 1.0], name=0))