There are two ways to hide the none option on the client side, using a JavaScript hack, or on the server side, by modifying the velocity templates that renders the select field. Let us see both, in different contexts.

First, we will see how to hide the none option on a given custom field with the ID 10000. All we have to do here is to add the following JavaScript snippet in the description of the field. As mentioned in the previous recipe, make sure the description is edited in the appropriate field configuration, if applicable:

<script type='text/javascript'> 
  JIRA.bind(JIRA.Events.NEW_CONTENT_ADDED, function (e, context) { 
    hideNone(); 
  }); 
  AJS.$(document).ready(function () { 
    hideNone(); 
  }); 
  function hideNone(){ 
    AJS.$("#customfield_10000 option[value='-1']").remove(); 
  } 
</script> 

Once this snippet is added, the none option will be hidden when the custom field with ID 10000 is edited.

Now, let us see how we can modify the velocity templates to do the same thing. Select Field is a system custom field that uses velocity templates to render the view and edit screens. In order to remove the none option, we need to modify the edit template.

Note that editing the template will remove the none option from all custom fields of type select. If you want to remove it from only certain select custom fields, don't forget to add extra checks in the velocity templates to do the same.

For any system custom field, you can find the associated classes and their velocity templates from the system-customfieldtypes-plugin.xml file, residing under the WEB-INF/classes folder.

In our case, we can find the following snippet related to select-field:

<customfield-type key="select" name="Select List (single choice)" 
 i18n-name-key="admin.customfield.type.select.name" 
 class="com.atlassian.jira.issue.customfields.impl.SelectCFType"> 
    <description key="admin.customfield.type.select.desc">
     A single select list with a configurable list of options.
    </description> 
 
    <resource type="download" name="customfieldpreview.png" 
      location="/images/customfieldpreview/select.png"> 
        <param name="source" value="webContextStatic"/> 
    </resource> 
 
    <resource type="velocity" name="view" 
      location="templates/plugins/fields/view/view-select.vm"/> 
    <resource type="velocity" name="edit" 
      location="templates/plugins/fields/edit/edit-select.vm"/>
    <resource type="velocity" name="xml" 
      location="templates/plugins/fields/xml/xml-select.vm"/> 
 
    <category>STANDARD</category> 
</customfield-type> 

As evident from the preceding snippet, the edit template for the select field is templates/plugins/fields/edit/edit-select.vm. That is the file we need to modify.

All we need to do now is to navigate to the file and remove the following lines:

#if (!$fieldLayoutItem || $fieldLayoutItem.required == false)
  <option value="-1">$i18n.getText("common.words.none")</option>
#else
  #if ( !$configs.default )
    <option value="">$i18n.getText("common.words.none")</option>
  #end
#end

The remaining code in the template must not be deleted. Restart JIRA to make the change effective.

There's more to it...