code: public void addQueryParam( String paramName, String value )
      {
          if ( _queryString == null )
          {
              _queryString = new InternalStringBuilder( "?" );
          }
          else
          {
              _queryString.append( '&' );
          }
          
          _queryString.append( paramName );
          
          if ( value != null )
          {
              _queryString.append( '=' ).append( value );
          }
      }
docs: Add a query parameter to the URI returned by {@link #getPath}.
  
  @param paramName the name of the query parameter.
  @param value the value of the query parameter, or <code>null</code> if there is no value.