code: public static String lookupIfEmpty( final String value,
                                          final Map<String, String> props,
                                          final String key ) {
          return value != null ? value : props.get(key);
      }
docs: Extracts value from map if given value is null.
  @param value current value
  @param props properties to extract value from
  @param key property name to extract
  @return initial value or value extracted from map