Java user

JavaUser.java

public class JavaUser {

    static class Address {
        String city;
    }

    private final String firstName;
    private final String lastName;
    private final List<Address> addresses;

    /**
     * If you want to make sure nothing is `null`
     * you have to check everything.
     */
    public static String getFirstCity(JavaUser user) {
        if(user != null && user.addresses != null && !user.addresses.isEmpty()) {
            for(Address address : user.addresses) {
                if(address.city != null) {
                    return address.city;
                }
            }
        }
        throw new IllegalArgumentException("This User has no cities!");
    }
}