Change the template for an empty post list

Hi All

Does anyone know how to change the template that shows when you insert a post list and choose a category of posts to show that is empty?

We're using a blog to promote tours so from time to time we will have categories with no posts (i.e. no upcoming tours)

All I can get is:

But I'm hoping to change the text to something like "No current tours scheduled"

Thanks so much!