*
   * <p>Unlike {@link Double#parseDouble(String)}, this method returns {@code null} instead of
   * throwing an exception if parsing fails. Valid inputs are exactly those accepted by {@link
   * Double#valueOf(String)}, except that leading and trailing whitespace is not permitted.
   *
   * <p>This implementation is likely to be faster than {@code Double.parseDouble} if many failures
   * are expected.
   *