Service-field empty when invoicing project or task

Hi,

since e-invoices are getting important, it would be a great idea, to prevent the service-field to be empty. But when invoicing a task or a project, that field ist genuinly not filled. It could (optionally) be filled out with the task-description (in case the option to fill it with the project-name is set to off).

And as another option it would be cool to prefill tasks with the service-field, while there would be a differenciation between service- and product-items. So invoices made out of projects or task don't have to be edited so much.