code: Parameter getCreateParameter(String name) {
  		if (this.parameters == null)
  			this.parameters = new HashMap<String, Parameter>();
  		Parameter param = this.parameters.get(name);
  		if (param == null) {
  			param = new Parameter(name);
  			this.parameters.put(name, param);
  		}
  		return param;
  	}
docs: Get or create, if not exists, a query parameter.
  @param name of the parameter
  @return a query parameter