Extra empty strings in expected values of Heatmap (#5)

No visual difference in actual and expected diagram . On checking in test_module.py found that , The list of expected values have 3 extra null strings.
Which results in error.

test_module.py

@@ -43,7 +43,7 @@ class HeatMapTestCase(unittest.TestCase):
     def test_heat_map_values(self):
         actual = [text.get_text() for text in self.ax.get_default_bbox_extra_artists() if isinstance(text, mpl.text.Text)]
         print(actual)
-        expected = ['0.0', '0.0', '-0.0', '0.0', '-0.1', '0.5', '0.0', '0.1', '0.1', '0.3', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.2', '0.1', '0.0', '0.2', '0.1', '0.0', '0.1', '-0.0', '-0.1', '0.1', '0.0', '0.2', '0.0', '0.1', '-0.0', '-0.0', '0.1', '0.0', '0.1', '0.4', '-0.0', '-0.0', '0.3', '0.2', '0.1', '-0.0', '0.0', '0.0', '-0.0', '-0.0', '-0.0', '0.2', '0.1', '0.1', '0.0', '0.0', '0.0', '0.0', '0.3', '0.0', '-0.0', '0.0', '-0.0', '-0.0', '-0.0', '0.0', '0.0', '-0.0', '0.0', '0.0', '0.0', '0.2', '0.0', '-0.0', '0.2', '0.1', '0.3', '0.2', '0.1', '-0.0', '-0.0', '-0.0', '-0.0', '0.1', '-0.1', '-0.1', '0.7', '0.0', '0.2', '0.1', '0.1', '-0.0', '0.0', '-0.0', '0.1', '', '', '']
+        expected = ['0.0', '0.0', '-0.0', '0.0', '-0.1', '0.5', '0.0', '0.1', '0.1', '0.3', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.2', '0.1', '0.0', '0.2', '0.1', '0.0', '0.1', '-0.0', '-0.1', '0.1', '0.0', '0.2', '0.0', '0.1', '-0.0', '-0.0', '0.1', '0.0', '0.1', '0.4', '-0.0', '-0.0', '0.3', '0.2', '0.1', '-0.0', '0.0', '0.0', '-0.0', '-0.0', '-0.0', '0.2', '0.1', '0.1', '0.0', '0.0', '0.0', '0.0', '0.3', '0.0', '-0.0', '0.0', '-0.0', '-0.0', '-0.0', '0.0', '0.0', '-0.0', '0.0', '0.0', '0.0', '0.2', '0.0', '-0.0', '0.2', '0.1', '0.3', '0.2', '0.1', '-0.0', '-0.0', '-0.0', '-0.0', '0.1', '-0.1', '-0.1', '0.7', '0.0', '0.2', '0.1', '0.1', '-0.0', '0.0', '-0.0', '0.1']
         self.assertEqual(actual, expected, "Expected differnt values in heat map.")
 
 if __name__ == "__main__":