Bug#926672: debbugs: 'bug' parameter is undefined for canonical URIs

Package: debbugs
Severity: normal

Dear Maintainer,

I noticed the HTML source of Bug# pages has the following backtrace on
bugs.debian.org:

<link rel="canonical" href="Program fragment delivered error ``The 'bug' parameter (undef) to Debbugs::CGI::bug_links was an 'undef', which is not one of the allowed types: scalar arrayref
 at /usr/local/lib/site_perl/Debbugs/CGI.pm line 435.
	Debbugs::CGI::bug_links(HASH(0x5619abd2dfc0)) called at template line 2
	eval 'package DTT; ;
#line 2 template
html_escape(bug_links{bug=>$bug_numsubject});' called at /usr/share/perl5/Text/Template.pm line 320
	Text::Template::fill_in(Text::Template=HASH(0x5619ae487a70), "PACKAGE", "DTT", "HASH", HASH(0x5619ae487dd0)) called at /usr/local/lib/site_perl/Debbugs/Text.pm line 188
	Debbugs::Text::fill_in_template("template", "cgi/bugreport", "variables", HASH(0x5619ae487608), "hole_var", HASH(0x5619ae487950)) called at /srv/bugs.debian.org/cgi-bin/bugreport.cgi line 458''">