Blackscreen when changing Activity in Android Studio

I have a ListView with clickable ListItems that display a Friend objects name and birthday. The onClick is supposed to start a new Activity with an edit page where you can change the name and birthday of said friend. For this I start a new activity with an Intent containing a Serialized Friend object.

The Activity works perfectly as it should as long as I don't add the Friend object to the intent:

intent.putExtra("friend", friendList.get(position) as Serializable)

but as soon as I add this line of code before starting the activity the screen just turns black. The program doesn't crash and there are no error messages, just a black screen.

MainActivity

    class MainActivity : Activity() {
    private var friendList : ArrayList<Friend> = arrayListOf()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        initButtons()
    }

    private fun initButtons() {
        val registerButton = findViewById<Button>(R.id.register_friend)
        registerButton.setOnClickListener {
            val name = findViewById<EditText>(R.id.name).text.toString()
            val birthday = findViewById<EditText>(R.id.birthday).text.toString()
            if(name != "" && birthday != "") {
                friendList.add(Friend(name,birthday))
            }
        }

        val showFriendsButton = findViewById<Button>(R.id.show_friends)
        showFriendsButton.setOnClickListener {
            val listView = findViewById<ListView>(R.id.friend_list_view)
            val adapter = FriendListAdapter(this, friendList)
            listView.adapter = adapter
            listView.choiceMode = ListView.CHOICE_MODE_SINGLE

            if(listView.getVisibility() == View.VISIBLE){
                listView.setVisibility(View.INVISIBLE)
            }else {
                listView.setVisibility(View.VISIBLE)
            }

            listView.setOnItemClickListener { parent, view, position, id ->
                val intent = Intent("android.intent.action.EDIT")
                intent.putExtra("friend", friendList.get(position) as Serializable)
                startActivity(intent)
            }
        }

    }
}

EditActivity

    class EditFriend : Activity(){

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.edit_friend)

        val friend: Friend = intent.getSerializableExtra("friend") as Friend
        findViewById<EditText>(R.id.name).setText(friend.name)
        findViewById<EditText>(R.id.birthday).setText(friend.birthday)

        val saveButton = findViewById<Button>(R.id.save)
        saveButton.setOnClickListener {
            val name = findViewById<EditText>(R.id.name).text.toString()
            val birthday = findViewById<EditText>(R.id.birthday).text.toString()
            if(name != "" && birthday != "") {
                friend.name = name
                friend.birthday = birthday
                finish()
            }
        }
    }

}

Friend

data class Friend(var name : String?, var birthday : String?) : Serializable