Minor simplification in DistanceMatrixDFCache

src/sensai/distance_metric.py

@@ -92,7 +92,7 @@ def get(self, key: Tuple[Union[str, int], Union[str, int]]) -> TValue:
         except KeyError:
             return None
         result = self.distance_df.iloc[pos1, pos2]
-        if result is None or np.isnan(result):
+        if np.isnan(result):
             return None
         return result