What is the chief purpose of line five in this code snippet?

override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_post_create)
    if (savedInstanceState != null) return
    val fragment = CreatePostFragment()
        supportFragmentManager
        .beginTransaction()
        .add(R.id. fragment_container, fragment)
        .commit()
}