Kotlin doesn’t allow nullable types by default. The problem right here is that the fragment manager can be null, and so if it is the whole expression will be null, but you’re casting it to a non-nullable YoutubePlayerFragment. The solution, simply, is to change the cast as YouTubePlayerFragment to a nullable type by instead doing as YouTubePlayerFragment?
I’d also personally suggest that you check out the Kotlin Documentation on Null Safety

Im implementing TouTube Api in my android Project. Im getting error in below line on “as” before YouTubePlayerFragment, “This cast can never succeed “. Im using to initialize youtube player in my fragment. I already tried android.enableJetifier=true in gradle.properties but its not helpfull

val youTubePlayerFragment = fragmentManager?.findFragmentById(R.id.vidVieW) as YouTubePlayerFragment
    youTubePlayerFragment?.initialize(Config.getYoutubeApiKey(),monInitializedListener)

Here is monInitializedListener code. It works fine when i used this in activity

monInitializedListener = object: YouTubePlayer.OnInitializedListener {
                    override fun onInitializationSuccess(
                        provider: YouTubePlayer.Provider,
                        player: YouTubePlayer,
                        wasRestored: Boolean
                    ) {
    
    
                        if (!wasRestored) {
                            mPlayer = player
    
                        }
    
                        // player.setPlayerStyle(YouTubePlayer.PlayerStyle.MINIMAL)
                        val mydef="BPGJUPcbQ58"
                        mPlayer?.loadVideo(mydef)
    
                        Toast.makeText(activity?.baseContext, "Fragment Visible", Toast.LENGTH_SHORT).show()
                    }
    
                    override fun onInitializationFailure(
                        p0: YouTubePlayer.Provider?,
                        p1: YouTubeInitializationResult?
                    ) {
                        Toast.makeText(activity?.applicationContext, "onInitializationFailure()", Toast.LENGTH_LONG).show()
                    }
    
    //
                }

This is a fragment inside my XML

<fragment
    
                android_name="com.google.android.youtube.player.YouTubePlayerFragment"
                android_id="@+id/vidVieW"
                android_layout_width="match_parent"
                android_layout_height="200dp"
                android_background="@drawable/orientation"
                app_layout_constraintEnd_toEndOf="parent"
                app_layout_constraintStart_toStartOf="parent"
                app_layout_constraintTop_toTopOf="parent"
    
                />

In logcat im getting this error

kotlin.TypeCastException: null cannot be cast to non-null type com.google.android.youtube.player.YouTubePlayerFragment