clear parameter if blank

Continued from #20. 

Previously, query parameter was as `?t=d&size=L`. So, the parameter is merged with the internal session parameters and would become as `?from=xxxx&to=xxxx&t=d&size=L` which results in stateful web design. 

But, in #20, I wanted to have RESTful design so that we can copy and paste the URL, and send it to somebody to see the same display. This patch fixes to be so.