code: public static RequestParameter valueExists(final String value)
     {
        return new RequestParameter("{" + RequestParameter.class.getName() + "_" + value + "_name}", value) {
           @Override
           public String toString()
           {
              return "RequestParameter.valueExists(\"" + value + "\")";
           }
        };
     }
docs: Create a {@link Condition} that matches only against the existence of a request parameter value matching the given
  pattern. The parameter name is ignored.
  <p>
  Parameter value expressions may be parameterized:
  <p>
  <code>
  RequestParameter.valueExists("guest")<br/>
  RequestParameter.valueExists("{username}")<br/>
  ...
  </code>
  
  @param name {@link ParameterizedPattern} matching the request parameter name.
  
  @see ConfigurationRuleParameterBuilder#where(String) {@link HttpServletRequest#getParameterMap()}