code: public URIBuilder addNullParameter( String key )
      {
          if ( key != null ) {
              queryParams.put( key, null );
          }
  
          return this;
      }
docs: Add a null query parameter (without any value). This will create a query string like : "key" (without '=' sign)
  
  @param key The parameter key (not url encoded)
  @return The builder