Sorry, the shown log entry doesn't say anything about the parameter list for the request which produced that log entry.

It shows your warning message (which indicates that parameter h wasn't set) with an empty string, a whitespace (or a possible undef in $h) at the position where $h should be interpolated... it's hard to guess, what caused that empty space between h: and t:.

The log doesn't say anything about the actual parameter list for the logged request.

What we see is the referrer's URL. That's the URL you were coming from (probably the URL you called before this logged one). And that URL contained parameter h in its query string (parameter list).

If I'm so badly wrong on this, please enlighten me and explain that log format to me.