check for blank LocalCredentials instead of None (#19)

libdyson/cloud/account.py

@@ -202,7 +202,7 @@ def devices(self) -> List[DysonDeviceInfo]:
         devices = []
         response = self.request("GET", API_PATH_DEVICES)
         for raw in response.json():
-            if raw.get("LocalCredentials") is None:
+            if not raw.get("LocalCredentials"):
                 # Lightcycle lights don't have LocalCredentials.
                 # They're not supported so just skip.
                 # See https://github.com/shenxn/libdyson/issues/2 for more info