类com.sunmeat.firebase.ChatMessage缺少一个没有参数的构造函数

Question

public ChatMessage(){
    // Don't delete!!!
    // othewice exception will occur: com.google.firebase.database.DatabaseException:
    // Class com.sunmeat.firebase.ChatMessage is missing a constructor with no arguments
}

ProGuard minifyEnabled true删除后程序无效。