code: @SuppressWarnings("rawtypes")
      protected String parseStringParameter(Map params, String paramName) {
          Object paramModel = params.get(paramName);
          if (paramModel == null) {
              return null;
          }
          if (!(paramModel instanceof SimpleScalar)) {
              throw new IllegalArgumentException(paramName + " must be string");
          }
          return ((SimpleScalar)paramModel).getAsString();
      }
docs: Parse string parameter.
  
  @param params the params
  @param paramName the param name
  @return the string