MonoScript.FromScriptableObject(this) returns null in CloudOnce 2.5.0

Hello, we are using Cloud Once for cloud save functionalities in our game. We have updated our game from Unity 4.6 to Unity 5.6 and then we updated Cloud Once to the latest version (2.5.0).
Everything seems to work, but every time I try to open CloudOnce editor window I receive ArgumentException: Invalid path error at this line:

Path.GetDirectoryName(AssetDatabase.GetAssetPath(MonoScript.FromScriptableObject(this)));

This seems due to the fact that MonoScript.FromScriptableObject(this) returns null.

Is it possibile that the update process has broken something? Is there any reason for MonoScript.FromScriptableObject(this) to return null?