My app database class
@Database(entities = {Detail.class}, version = Constant.DATABASE_VERSION) public abstract class AppDatabase extends RoomDatabase {
Not in the case of OP, but this also happens when you mistakenly use implementation instead of annotationProcessor like this:
implementation "android.arch.persistence.room:compiler:x.x.x"
Instead of this:
annotationProcessor "android.arch.persistence.room:compiler:x.x.x"