updated ProductList.filter_clouds to return same list if cloud_cover is None

sen2chain/tiles.py

@@ -100,7 +100,10 @@ class ProductsList:
         """
         filtered = ProductsList()
         for k, v in self._dict.items():
-            if cover_min <= v["cloud_cover"] <= cover_max:
+            if v["cloud_cover"]:
+                if cover_min <= v["cloud_cover"] <= cover_max:
+                    filtered[k] = {"date": v["date"], "cloud_cover": v["cloud_cover"]}
+            else:
                 filtered[k] = {"date": v["date"], "cloud_cover": v["cloud_cover"]}
         return filtered