Fix handling of url params with empty value so that they are treated as null in all cases.  Previously, if multiple url param values were given and one was empty, then the result of getParameterValues() would return [value,""], which would screw-up things like date filtering.
Fix handling of url params with empty value so that they are treated
as null in all cases.  Previously, if multiple url param values were
given and one was empty, then the result of getParameterValues() would
return [value,""], which would screw-up things like date filtering.

aaronbinns/tnh,aaronbinns/tnh