code: public static String mandatoryAttributeValue(Map<Object, Object> attributeMap, String name) {
          Object value = attributeMap.get(name);
          if (value != null) {
              String text = value.toString();
              if (!Strings.isBlank(text)) {
                  return text;
              }
          }
          throw new IllegalArgumentException("The attribute value '" + name + "' did not get passed on from the previous wizard page");
      }
docs: Returns the mandatory String value of the given name
  
  @throws IllegalArgumentException if the value is not available in the given attribute map