diff --git a/analytics/analytics/analytic_unit_manager.py b/analytics/analytics/analytic_unit_manager.py
index 89d6c7c..4025951 100644
--- a/analytics/analytics/analytic_unit_manager.py
+++ b/analytics/analytics/analytic_unit_manager.py
@@ -32,6 +32,7 @@ def prepare_data(data: list):
     """
     data = pd.DataFrame(data, columns=['timestamp', 'value'])
     data['timestamp'] = pd.to_datetime(data['timestamp'], unit='ms')
+    data.fillna(value = np.nan, inplace = True)
     if not np.isnan(data['value'].min()):
         data['value'] = data['value'] - min(data['value'])
 
diff --git a/analytics/tests/test_dataset.py b/analytics/tests/test_dataset.py
index 99eb3b4..ac66919 100644
--- a/analytics/tests/test_dataset.py
+++ b/analytics/tests/test_dataset.py
@@ -115,6 +115,16 @@ class TestDataset(unittest.TestCase):
             data = prepare_data(data)
         except ValueError:
             self.fail('Model {} raised unexpectedly'.format(model_name))
+    
+    def test_prepare_data_output_fon_nan(self):
+        data_nan = [[1523889000000, np.NaN], [1523889000001, np.NaN], [1523889000002, np.NaN]]
+        data_none = [[1523889000000, None], [1523889000001, None], [1523889000002, None]]
+        return_data_nan = prepare_data(data_nan)
+        return_data_none = prepare_data(data_none)
+        for item in return_data_nan:
+            self.assertTrue(np.isnan(item.value))
+        for item in return_data_none:
+            self.assertTrue(np.isnan(item.value))
 
 if __name__ == '__main__':
     unittest.main()