After a user deletes his avatar, "User Avatar" is not correctly displayed

Steps to reproduce:

1. Create an user
2. Log in with that user
3. Add a profile image
4. Delete the image from Profile and do not select the default image as avatar (just delete the inserted image)
5. Create a page
6. Edit that page in WYSIWYG mode
7. Click on "Macro"
8. Search for "User avatar" macro and then click on it
9. Complete all the fields (with your username, the current username - that one with the deleted image)
10. Click on "Insert Macro"

The inserted image is not correctly displayed, because instead of the default image, you see a broken image.