code: private static String buildParentString(final String tag,
              final String tail) {
          if (tail.isEmpty()) {
              return tag;
          } else {
              return tag + " " + tail;
          }
      }
docs: The parent can only take one string. If we need to, concatenate the
  strings. The argument tag should never be empty, but tail could be.
  
  @param tag tag string
  @param tail tail string
  @return the constructed string