code: public static Query valueExists(final String valuePattern)
     {
        Assert.notNull(valuePattern, "Parameter value pattern must not be null.");
  
        return new Query() {
           final ParameterizedPatternParser pattern = new RegexParameterizedPatternParser(valuePattern);
  
           @Override
           public boolean evaluateHttp(final HttpServletRewrite event, final EvaluationContext context)
           {
              QueryStringBuilder queryString = QueryStringBuilder.createFromEncoded(event.getAddress().getQuery())
                       .decode();
  
              for (String name : queryString.getParameterNames()) {
  
                 for (String value : queryString.getParameterValues(name)) {
                    if (value != null && pattern.parse(value).submit(event, context))
                    {
                       return true;
                    }
                 }
              }
  
              return false;
           }
  
           @Override
           public String toString()
           {
              return "Query.valueExists(\"" + valuePattern + "\")";
           }
  
           @Override
           public Set<String> getRequiredParameterNames()
           {
              return pattern.getRequiredParameterNames();
           }
  
           @Override
           public void setParameterStore(ParameterStore store)
           {
              pattern.setParameterStore(store);
           }
        };
     }
docs: Create a {@link Condition} asserting the existence of specific parameter values within the current
  {@link Address#getQuery()}.
  
  @param pattern {@link ParameterizedPattern} matching query parameter values of the current
  {@link Address#getQuery()}.
  
  @see ConfigurationRuleParameterBuilder#where(String)