Attempt to invoke virtual method on a null object reference at

Question

I have this code, which, according to my idea, should set the background for nicknames in the chat when you turn on the custom background in the chat. Current file - AppearanceFragment.kt

package com.twoeightnine.root.xvii.features.appearance

import android.graphics.drawable.GradientDrawable
import android.os.Bundle
import android.util.TypedValue
import android.view.View
import android.widget.CompoundButton
import android.widget.TextView
import android.content.res.ColorStateList
import android.graphics.Color
import androidx.core.view.isVisible
import com.twoeightnine.root.xvii.base.BaseActivity
import android.view.WindowManager;
import android.graphics.drawable.Drawable
import android.view.LayoutInflater
import androidx.appcompat.app.AppCompatActivity
import androidx.core.content.ContextCompat
import com.flask.colorpicker.ColorPickerView
import com.flask.colorpicker.builder.ColorPickerDialogBuilder
import com.twoeightnine.root.xvii.R
import com.twoeightnine.root.xvii.base.BaseFragment
import com.twoeightnine.root.xvii.chats.attachments.gallery.GalleryFragment
import com.twoeightnine.root.xvii.extensions.load
import com.twoeightnine.root.xvii.managers.Prefs
import com.twoeightnine.root.xvii.uikit.Munch
import com.twoeightnine.root.xvii.uikit.paint
import com.twoeightnine.root.xvii.utils.*
import com.twoeightnine.root.xvii.views.LoadingDialog
import global.msnthrp.xvii.uikit.extensions.applyBottomInsetPadding
import global.msnthrp.xvii.uikit.extensions.hide
import global.msnthrp.xvii.uikit.extensions.lowerIf
import global.msnthrp.xvii.uikit.extensions.setVisible
import global.msnthrp.xvii.uikit.utils.color.ColorUtils
import kotlinx.android.synthetic.main.chat_input_panel.*
import kotlinx.android.synthetic.main.fragment_appearance.*
import kotlinx.android.synthetic.main.item_message_in_chat.*
import kotlinx.android.synthetic.main.view_appearance_sample.*
import kotlinx.android.synthetic.main.view_appearance_sample.view.*
import java.io.File





class AppearanceFragment : BaseFragment() {
//...
      private fun setback() {
         nickname.setBackgroundResource(R.drawable.nick_shape)
        }
      private fun delback() {
            nickname.setBackgroundResource(R.drawable.nick_shape_wo)
      }
      private fun initViews() {
        isLightBefore = Prefs.isLightTheme
        switchLightTheme.onCheckedListener = CompoundButton.OnCheckedChangeListener { _, b ->
            applyColors()
        }
        switchLightTheme.isChecked = isLightBefore
        if (Prefs.chatBack.isNotEmpty()) {
            updatePhoto(Prefs.chatBack)
        }
        btnGallery.setOnClickListener { openGallery() }
        csThemeColor.setOnClickListener {
            showColorPicker(currentColor) { color ->
                currentColor = color
                applyColors()
            }
        }



        switchChatBack.onCheckedListener = CompoundButton.OnCheckedChangeListener { _, isChecked ->
            llCustomBack.setVisible(isChecked)
            setback()
            nickname.setBackgroundResource(R.drawable.nick_shape);
            if (!isChecked) {
                deletePhoto()
                delback()
               // nickname.setBackgroundResource(R.drawable.nick_shape_wo);

            }


        }

when starting the program it gives the following error java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setBackgroundResource(int)" on a null object reference at com.twoeightnine.root.xvii.features.appearance.Appea ranceFragment.setback(AppearanceFragment.kt: 239)

Tried to create in activity and not in fragment but not successfull