Manipulates the resultant URL by adding this key value pair.
Assembly: Endeca.Navigation (Module: Endeca.Navigation) Version: 0.0.0.0
This method will overwrite ANY of the original parameters with the same key and any other parameter that got added by this same method previously with the same key. In addition, it is assumed that val is decoded and will encode the value as x-www-form-urlencoded on output. Values that are null or equal to "" will be skipped so that this method can be blindly called without having to check if the value is present.