What is ID of select list "None" option?

[Hisamitsu Koga]

I want to know ID of select list "None" option. Could you someone let me know what ID of

select list "None" option is.

[Volodymyr Krupach @BrizoIT]

I guess there is no id. It's just empty value option.

[Hisamitsu Koga]

Thank you for your prompt comment.

[Heiko Gerlach]

Seems you are asking for a Multi/Single Selection of a customfield. For customfields you need the option value, not the id. Option value for "none" is -1.

[pbielicki_atlassian]

It depends what you mean by ID. I assume you're talking about HTML select e.g:

<select name="options">
  <option value="none">None</option>
  <option value="one">One</option>
  <option value="two">Two</option>
  <option value="three">Three</option>
</select>

Value of None option is "none" in this case but it can be anything and there is no ID. You can have

<option value="0" id="none">None</option>

in such case value of None is 0 and ID is "none". 

There is no generic answer for your question I'm afraid. You would need to check the output HTML to see the concrete values.