Don't understand why I'm getting this error. Any suggestions/guidance would be great - api

Question

package com.example.myapplication
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import android.view.View
import androidx.recyclerview.widget.LinearLayoutManager
import com.example.myapplication.MainModel
import com.example.myapplication.MovieAdapter
import com.example.myapplication.R
import com.example.myapplication.retrofit.ApiService
import kotlinx.android.synthetic.main.activity_detail.*
import kotlinx.android.synthetic.main.activity_main.*
import retrofit2.Call
import retrofit2.Callback
import retrofit2.Response
class MainActivity : AppCompatActivity() {
private val TAG: String = "MainActivity"
private lateinit var movieAdapter: MovieAdapter
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
supportActionBar!!.title = "Avengers"
setupRecyclerView()
getDataFromApi()
}
private fun getDataFromApi() {
showLoading(true)
ApiService.endpoint.data()
.enqueue(object : Callback<MainModel> {
override fun onFailure(call: Call<MainModel>, t: Throwable) {
printLog(t.toString())
showLoading(false)
}
override fun onResponse(
call: Call<MainModel>,
response: Response<MainModel>
) {
showLoading(false)
if (response.isSuccessful) {
showResult(response.body()!!)
}
}
})
}
private fun printLog(message: String) {
Log.d(TAG, message)
}
private fun showLoading(loading: Boolean) {
when (loading) {
true -> progressBar.visibility = View.VISIBLE
false -> progressBar.visibility = View.GONE
}
}
private fun showResult(results: MainModel) {
for (result in results.result) printLog("title: ${result.artistId}")
movieAdapter.setData(results.result)
}
private fun setupRecyclerView(){
movieAdapter = MovieAdapter(arrayListOf(), object : MovieAdapter.OnAdapterListener {
override fun onClick(result: MainModel.Result) {
recyclerView.apply {
layoutManager = LinearLayoutManager(context)
adapter = movieAdapter
}
}
})
}
}
This is the error:
2022-08-13 22:41:43.360 14628-14628/com.example.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.myapplication, PID: 14628
java.lang.NullPointerException: Attempt to invoke virtual method 'java.util.Iterator java.util.ArrayList.iterator()' on a null object reference
at com.example.myapplication.MainActivity.showResult(MainActivity.kt:64)
at com.example.myapplication.MainActivity.access$showResult(MainActivity.kt:18)
at com.example.myapplication.MainActivity$getDataFromApi$1.onResponse(MainActivity.kt:46)
at retrofit2.DefaultCallAdapterFactory$ExecutorCallbackCall$1.lambda$onResponse$0$retrofit2-DefaultCallAdapterFactory$ExecutorCallbackCall$1(DefaultCallAdapterFactory.java:89)
at retrofit2.DefaultCallAdapterFactory$ExecutorCallbackCall$1$$ExternalSyntheticLambda1.run(Unknown Source:6)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)