config-servlet/src/main/java/org/ocpsoft/rewrite/servlet/config/RequestParameter.java
public static RequestParameter exists(final String name)
   {
      return new RequestParameter(name, "{" + RequestParameter.class.getName() + "_" + name + "_value}") {
         @Override
         public String toString()
         {
            return "RequestParameter.exists(\"" + name + "\")";
         }
      };
   }
public static RequestParameter exists(final String name)
   {
      return new RequestParameter(name, "{" + RequestParameter.class.getName() + "_" + name + "_value}") {
         @Override
         public String toString()
         {
            return "RequestParameter.exists(\"" + name + "\")";
         }
      };
   }
Create a {@link Condition} that matches against the existence of a request parameter with a name matching the
given pattern. The parameter value is ignored.
<p>
Parameter name expressions may be parameterized:
<p>
<code>
RequestParameter.exists("username")<br/>
RequestParameter.exists("{name}")<br/>
...
</code>

@param name {@link ParameterizedPattern} matching the request parameter name.

@see ConfigurationRuleParameterBuilder#where(String) {@link HttpServletRequest#getParameterMap()}