Add support for multiuser custom field

[capiscuas]

Hi, i have a Validate custom button and I'd like to assign it so that the user that clicks on the button, gets added to a multiuser custom field of that issue called 'Validators'.
Problem is that multiuser/even users type custom fields are not filled in by the plugin, any hint? Is there a similar plugin doing this?

redmine_customize/app/views/custom_buttons/_form.html.erb

Line 97 in 7b8e085

<p><%= custom_field_tag_with_label :custom_button, value %></p>