Search Result with querystring parameters

I trying to use Query Variables and specific one Im trying to use is {QueryString.}

I have edited my Search Result Web Part and used the query builder. My query is simple and works just fine inside the builder:

(contentclass:STS_ListItem OR IsDocument:True) AND owstaxidmetadataalltagsinfo:{QueryString.MyParameter1}

When I use the Test tab inside the builder I get a result.

If I save the query and then browse the searchpage like this: http://myurl.com/search.aspx?MyParameter1=Test I get "nothing here matches your search".

If I check my logs I find the following error:

QueryTemplateHelper: Cannot replace parameters in template. The value for parameter 
  QueryString.MyParameter1 is missing. Parameter : QueryString.MyParameter1, 
  Template: (contentclass:STS_ListItem OR IsDocument:True) {QueryString.MyParameter1}.