Allow Entry URI Format to be conditionally blank (no URL)

[timkelty]

Several times we've wanted a fully dynamic "Entry URI Format", where conditionally, some entries in a section (usually by depth), don't have URLs.

Making this "Entry URI Format" something like this has a peculiar effect:

{% if level == 1 %}projects/{slug}{% endif %}

I want entries with level 2 to have no url, but instead they seem to get a homepage URL (even if there is already a homepage single). Subsequent level 2 entries will fail because of the occupied URL.