private static OptionalLong parse(final String string) {
        if (string == null) {
            return OptionalLong.empty();
        } else {
            try {
                if (NullSafe.isNonBlankString(string)) {
                    // Parse numeric part of dir name.
                    return OptionalLong.of(Long.parseLong(string));
                } else {
                    return OptionalLong.empty();
                }
            } catch (final NumberFormatException e) {
                return OptionalLong.empty();
            }
        }
    }
Extract the number represented by the supplied `0` padded string.

@param string A directory name.
@return The long part of the string if found, else empty.
stroom-proxy/stroom-proxy-app/src/main/java/stroom/proxy/app/handler/DirUtil.java