Add an object to a 1:M relation in the Users table

Android
1

My Users table has a 1:M relation with another table Paper. When adding a new object with the code below:

List<Paper> list = (List<Paper>) user.getProperty("paper");
list.add(somePaperObject);
Backendless.UserService.update(user);

I get an unchecked cast error at line:1. And the app crashes due to the cast (only sometimes). Is there a better way to add an object to a 1:M relation in the Users table?

2

See the paragraph starting with: “There is a special consideration for a user property containing a collection of related data” on this page:

https://backendless.com/documentation/users/android/users_user_properties.htm