All options optional in one of sets

**Describe the bug**
I have two parameter sets. One has only one option, bool list, works fine:

`mytool new --list # works fine`

The other set works fine, while it has at least one required option

`mytool new --template "default"`

But I want all the options in my second set to be optional. I'd like to run

`mytool new`

and expect the second set is picked up, with "template" option set to "default". I cannot achieve it.

**To Reproduce**
https://dotnetfiddle.net/VE1xFs

**Expected behavior**
When one of the sets has all options optional, with defaults, it is automatically picked when no command-line arguments are provided.

從連結的 .NET Fiddle 重現器開始，比較未提供任何引數時的參數集選擇與存在必要選項時的選擇。追蹤剖析器如何處理一個全部為選用項目的參數集及其預設值。完成的標準是 `mytool new` 選取該參數集，並將 `template` 設定為 `default`，同時現有的必要選項和 `--list` 案例繼續正常運作。

由索引模型根據 Issue 內容生成。