Unity C#で　keynotfoundexception: the given key was not present in the dictionaryのエラーが数カ所

前提

Unity2019.3.12f1を使用しています。

エラーメッセージ

KeyNotFoundException: The given key was not present in the dictionary.
System.Collections.Generic.Dictionary`2[TKey,TValue].get_Item (TKey key) (at <437ba245d8404784b9fbab9b439ac908>:0)

該当のソースコード

C#
1 private const char SEPARATE_SUBSCENE = '#';
2    private Dictionary<string, Queue<string>> _subScenes =
3           new Dictionary<string, Queue<string>>();
4
5    private const string COMMAND_JUMP = "jump_to";
6    private void JumpTo(string parameter)
7    {
8        parameter = parameter.Substring(parameter.IndexOf('"') + 1, parameter.LastIndexOf('"') - parameter.IndexOf('"') - 1);
9        **_pageQueue = _subScenes[parameter];**
10    }

C#
1    private void SelectButtonOnClick(string label)
2    {
3        foreach (Button button in _selectButtonList) Destroy(button.gameObject);
4        _selectButtonList.Clear();
5        **JumpTo('"' + label + '"');**
6        ShowNextPage();
7    }

C#
1    private void SetSelectButton(string name, string cmd, string parameter)
2    {
3        cmd = cmd.Replace(COMMAND_SELECT, "");
4        name = name.Substring(name.IndexOf('"') + 1, name.LastIndexOf('"') - name.IndexOf('"') - 1);
5        Button button = _selectButtonList.Find(n => n.name == name);
6        if (button == null)
7        {
8            button = Instantiate(Resources.Load<Button>(prefabsDirectory + SELECT_BUTTON_PREFAB), selectButtons.transform);
9            button.name = name;
10            **button.onClick.AddListener(() => SelectButtonOnClick(name));**
11            _selectButtonList.Add(button);
12        }
13        SetImage(cmd, parameter, button.image);
14    }