interface UserMapper {

    @Select("SELECT userId, phoneNumber FROM users WHERE phoneNumber=#{number} LIMIT 1")
    fun getUserByPhoneNumber(number: String?): User
}

public class User {

        private int userId;
        private String phoneNumber;
}

val user = userMapper!!.getUserByPhoneNumber(phonenumber)
if (user != null) {
    doSomething()
} else {
    doOtherthing()
}

[WARNING] Condition 'user != null' is always 'true'