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#!/usr/bin/perl -wT

...
}else{
    print "content-type:text/html; charset=utf-8\n\n";
}

#!/usr/bin/perl -wT

...
}else{
    print "content-type:application/xhtml+xml; charset=utf-8\n\n";
}

Use of uninitialized value $ENV{"HTTP_ACCEPT"}...