AppExecutor | 应用线程池，可以指定任务的优先级，完全kotlin

I am working through a school book example as on how to write data into a SQlite database using Room in Android. Apparently, we cannot write data into the database from the main-thread, but we need a background-thread for this. In my book, what we do is, we create an extra class AppExecutors with the following content:

So I am relatively new to programming, and I have been working on this task app, where I want to save the data such as task name and more, given by the user. I am trying to accomplish this using Room. Now, initially, when I tried to do it, the app would crash since I was doing everything on the main thread probably. So, after a little research, I came to AsyncTask, but that is outdated. Now finally I have come across the Executer. I created a class for it, but I am a little unsure as to how I can implement it in my app. This is what I did :

Entity Class :

Wrote a method for creating and overlaying a route between two points. The problem is that when it's triggered in normal mode (without breakpoints), it causes NullPointerException or IllegalStateException, but when I run my app in Debug-mode it throws nothing and works correctly. I'm sorry for my english (i'm from Russia) and I apologize for formulation of the question, I'm still not really familiar with stackoverflow.

Here is my method:

I am trying to do custom work manager initialisation. I do not want the work manager to get initialised at the beginning, I want to initialise only if login is success. But I always get the below exception even though work manager is not initialised:

I'm following the Github Browser app tutorial to build my project without using databinding. The display is just blank only showing the navigation view. I cannot figure out where I am going wrong. I tried to debug and all its showing is that result is null. No errors.

ViewModel.java:

The following code is from the project.

The author design var toyList as LiveData>? in MainViewModel.

I think that it would be better if I design var toyList as LiveData>, how can I do ?

The following code is based the project https://github.com/enpassio/Databinding

I hope to determine whether exist a record by id, so I write the following code.

I think my code is not good, is these a simple way to determine whether exist a record by id using Room?

Can I directly a SQl and return Booean with @Dao? If so, how can I do?

Code

I'm struggling for a certain amount of time so I decided to ask for help here... I'm using almost the as same architecture as Google sample: GithubBrowserSample.

In the test of one of my fragment (androidTest) I encounter this error:

I'm using almost the as same architecture as Google sample: GithubBrowserSample.

This field is injected in my Fragment class: