diff --git a/localizationkit/tests/comment_similarity.py b/localizationkit/tests/comment_similarity.py
index 2012a6c..26b407d 100644
--- a/localizationkit/tests/comment_similarity.py
+++ b/localizationkit/tests/comment_similarity.py
@@ -24,6 +24,9 @@ class CheckCommentSimilarity(LocalizationTestCase):
         violations = []
 
         for string in self.collection.strings_for_language(self.configuration.default_language()):
+            if string.value is None or string.comment is None:
+                continue
+
             similarity = difflib.SequenceMatcher(None, string.value, string.comment).ratio()
 
             if similarity > maximum_comment_similarity_ratio:
diff --git a/localizationkit/tests/test_case.py b/localizationkit/tests/test_case.py
index e56ae03..07d319a 100644
--- a/localizationkit/tests/test_case.py
+++ b/localizationkit/tests/test_case.py
@@ -68,7 +68,7 @@ class LocalizationTestCase(abc.ABC):
         try:
             violations = self.run_test()
 
-            if not violations:
+            if violations is None:
                 raise Exception(f"Failed to get exceptions from test: {self.__class__.name()}")
 
             if len(violations):