Firebase Storage - Can't get download URL

[kubawich]

I've got this simple code, what I've got from running this is
FLTFirebaseStorage: An unknown error occurred while calling method Reference#getDownloadURL
flutter: [firebase_storage/unknown] Failed to retrieve a download URL.
I've already tried using getDownloadURL() in various different configurations, but non of these worked, every time giving me the same error. How can I fix this?
Future<void> updateLogoInFirestore(File file, String url) async { try { final storageRef = FirebaseStorage.instance.ref(); final uploadTask = storageRef.child("Logos/${employer.value.companyFullName}"); var a = await storageRef.getDownloadURL(); print(a); } catch (e) { print(e); } }