Any way possible for replacing none with custom value when we are using query variable to generate link

Hi ,
I am trying to generate a link using query variable in grafana dashboard graph,
eg : http://example.com?q=${query_variable}

when query_variable is none i mean when query returns no value , is there a way to replace query_variable by empty string (http://example.com?q="")

Behaviour right now : it doesn’t replace with any value

Any help would be greatly appreciated .

Thanks.