code: public String getParamString(String paramName) {
          Object paramValue = getParam(paramName);
          if (paramValue == null) {
              return null;
          }
          return paramValue.toString();
      }
docs: Get the value of the parameter with the given name belonging to this service as a
  String. If the parameter is not found, null is returned.
  
  @param paramName Name of parameter to find.
  @return          Parameter found as a String if found, otherwise null.