Question: [Type mismatch: inferred type is ArrayList<com.hariscm.ngobrolind.db.data.Message> but ArrayList<hariscmtham.letschat.db.data.Message!>! was expected](https://i.stack.imgur.com/qGurk.png)

Answer: 
According to error message, one of the Message data structure imported from `com.hariscm.ngobrolind.db.data.Message` but another one imported from `hariscmtham.letschat.db.data.Message`. Make sure both of them imported from the same package.
If that didn't resolve the issue, check nullability of your ArrayList.
I would suggest to look at the imports of the class, make sure you have imported `Message` class from `com.hariscm.ngobrolind.db.data.Message`.