code: public final T getUnique(final T defaultValue) {
          try {
              final T result = getUnique();
              if (result != null) {
                  return result;
              }
          } catch (final Throwable ex) {
              // ignore
          }
          return defaultValue;
      }
docs: Terminal operation returning the only element in this Stream, or the default value
  specified if there are no elements, multiple elements or an Exception occurs.
  
  @param defaultValue
  the default value to return if a unique value cannot be extracted
  @return the only element in this Stream, or the default value in case that element does not
  exist, there are multiple elements or an Exception occurs