I am facing trouble in adding data using SQLite database - android-studio

Question

I am trying to insert some information of cars using 3 EditTexts in my xml page and by creating table SQLite database and an error occurs in logcat:
Process: com.example.sqlite, PID: 7264
java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference
at android.widget.Toast.<init>(Toast.java:102)
at android.widget.Toast.makeText(Toast.java:259)
at com.example.sqlite.MyDatabaseHelper.addCar(MyDatabaseHelper.kt:58)
at com.example.sqlite.AddActivity$onCreate$1.onClick(AddActivity.kt:15)
at android.view.View.performClick(View.java:5198)
at android.view.View$PerformClick.run(View.java:21147)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
here is my Database Creation:
private val context:Context? = null
private const val TABLE_NAME = "my_CarShow"
private const val COLUMN_ID = "_id"
private const val COLUMN_NAME = "car_name"
private const val COLUMN_TYPE = "car_type"
private const val COLUMN_MODEL = "car_model"
const val DATABASE_NAME: String = "CarShow.db"
const val DATABASE_VERSION: Int = 1
class MyDatabaseHelper(context: Context?) : SQLiteOpenHelper(context, DATABASE_NAME, null, DATABASE_VERSION) {
override fun onCreate(db: SQLiteDatabase?) {
val query = "CREATE TABLE " + TABLE_NAME +
" (" + COLUMN_ID + " INTEGER PRIMARY KEY," +
COLUMN_NAME + " TEXT," +
COLUMN_TYPE + " TEXT," +
COLUMN_MODEL + " INTEGER)"
db!!.execSQL(query)
}
override fun onUpgrade(db: SQLiteDatabase?, oldVersion: Int, newVersion: Int) {
db!!.execSQL("DROP TABLE IF EXISTS $TABLE_NAME")
onCreate(db)
}
fun addCar(name:String, type:String, model:String){
var db = this.writableDatabase
var cv = ContentValues()
cv.put(COLUMN_NAME,name)
cv.put(COLUMN_TYPE,type)
cv.put(COLUMN_MODEL,model)
var result = db.insert(TABLE_NAME,null, cv)
if (result == -1L){
Toast.makeText(context,"Failed",Toast.LENGTH_SHORT).show()
}
else{
Toast.makeText(context,"Added Successfully",Toast.LENGTH_SHORT).show()
}
}
}
and here is the activity that the data must be iserted or added :
class AddActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_add)
add_button.setOnClickListener {
val myDb = MyDatabaseHelper(this)
myDb.addCar(name_input.text.toString(),
type_input.text.toString(),
model_input.text.toString())
}
}
}
what can I do to solve this error?
Thanks for your attention