You're getting a blank name/value pair. The general format of an HTTP get request is

url?name1=value1&name2=value2&name3=value3
[download]

CGI.pm is probably first splitting the query string on & chars, and then subsequently splitting those chunks on = chars, and associating each of those two pieces as the name and value of a key in a hash. If you put an & char at the start of the query string, CGI.pm is going to get confused, as it'll have an empty string that it tries to split in an = char, and then it will try to stick those values (that it didn't get) into a hash.