Cannot select 'Component Lead' as a Default Assignee for a project

[Sergey Shmarkatyuk]

I want to select 'Component Lead' as a Default Assignee for a project, but for some reason I can't. Documentation says that 

If the component leader is not permitted to be assigned to issues in the permission scheme, this option will be disabled and will say "Component Lead is not allowed to be assigned issues". The Component Lead option will also not be available if the component does not have a lead assigned to the component. Instead under this option it will say "Component does not have a lead."

I checked and all users that are mentioned in the field 'Component Lead' for the corresponding component have 'Assignable User' rights. Also I checked that there are no components with empty Component Lead. Do you have any ideas what else could be causing 'Component Lead' option missing from the 'Default Assignee' field of a project?

[Joseph Pitt]

If you have component leads you can setup JIRA for the 'default assignee' will pick the component lead automatically. see https://confluence.atlassian.com/adminjiraserver072/managing-components-829827054.html 

[Sergey Shmarkatyuk]

But how do I do this if I have only 'Project Lead' and 'Unassigned' as the options for the 'Default Assignee' field on project roles configuration page?