Package version tested: 2.4.7-1ubuntu4
Expected behavior: site names should be whitespace-tolerant.
[Side note: site names should probably also not require the .conf extension, as there should be no other normal files in sites-enabled/ -- just filtering out directories (for version control systems which wrongly version sites-enabled rather than sites-available) should suffice. This also eliminates the complicated logic where a2ensite looks both for "$1" and "$1.conf", unless we want to keep that for historical compatibility reasons. ]
Observed behavior: a2ensite breaks when there is whitespace in a site name.
Steps to reproduce:
$ sudo su -
# cp -a 000-default.conf '001 filename with whitespace.conf'
# a2ensite '001 filename with whitespace.conf'
ERROR: Site 001 does not exist!
ERROR: Site filename does not exist!
ERROR: Site with does not exist!
ERROR: Site whitespace does not exist!