code: public String getSingleValue(final String propertyName) {
          Preconditions.checkNotNull(propertyName);
          List<String> values = getValues(propertyName);
          if (values == null || values.size() < 1) {
              return null;
          }
          return values.get(0);
      }
docs: A helper method for getting the value of single valued properties. Returns
  null if the property does not exist.
  
  @param propertyName name of the property as defined by the bean's schema.
  @return final String representations of the property that conforms to
  its type as defined by the bean's schema.