diff --git a/image_prediction/estimator/preprocessor/preprocessor.py b/image_prediction/estimator/preprocessor/preprocessor.py
index e5da175..3959b51 100644
--- a/image_prediction/estimator/preprocessor/preprocessor.py
+++ b/image_prediction/estimator/preprocessor/preprocessor.py
@@ -2,10 +2,11 @@ import abc
 
 
 class Preprocessor(abc.ABC):
+
     @staticmethod
     @abc.abstractmethod
     def preprocess(batch):
-        pass
+        raise NotImplementedError
 
     def __call__(self, batch):
         return self.preprocess(batch)
diff --git a/image_prediction/estimator/preprocessor/preprocessors/basic.py b/image_prediction/estimator/preprocessor/preprocessors/basic.py
index f8e5943..03e94e6 100644
--- a/image_prediction/estimator/preprocessor/preprocessors/basic.py
+++ b/image_prediction/estimator/preprocessor/preprocessors/basic.py
@@ -8,6 +8,3 @@ class BasicPreprocessor(Preprocessor):
     @staticmethod
     def preprocess(images):
         return images_to_batch_tensor(images)
-
-    def __call__(self, images):
-        return self.preprocess(images)
diff --git a/image_prediction/extractor_classifier/extractor_classifier.py b/image_prediction/extractor_classifier/extractor_classifier.py
index 930dfb1..1206756 100644
--- a/image_prediction/extractor_classifier/extractor_classifier.py
+++ b/image_prediction/extractor_classifier/extractor_classifier.py
@@ -15,10 +15,7 @@ class ExtractorClassifier:
         self.extractor = image_extractor
 
     def __process_batch(self, batch):
-        try:
-            images, metadata = zip(*batch)
-        except ValueError:
-            return []
+        images, metadata = zip(*batch)
 
         predictions = self.classifier(images)
         responses = ({"prediction": prd, **mdt} for prd, mdt in zip(predictions, metadata))
diff --git a/image_prediction/formatter/formatter.py b/image_prediction/formatter/formatter.py
index 2d71ee5..a22bc1d 100644
--- a/image_prediction/formatter/formatter.py
+++ b/image_prediction/formatter/formatter.py
@@ -2,5 +2,7 @@ import abc
 
 
 class Formatter(abc.ABC):
+
+    @abc.abstractmethod
     def format(self, info: dict):
-        pass
+        raise NotImplementedError