FP: Possible null dereference

[ben-manes]

Possible null dereference in CaffeineSpec.parseDuration().
The expression value.length() may fail with NullPointerException as value
can be null at this location.

static long parseDuration(String key, String value) {
  requireArgument(value != null && !value.isEmpty(), "value of key %s omitted", key);
  return parseLong(key, value.substring(0, value.length() - 1));
}

where requireArgument is defined as,

static void requireArgument(boolean expression, String template, Object... args) {
  if (!expression) {
    throw new IllegalArgumentException(String.format(template, args));
  }
}

Resulting in a null check prior to value.length() so that it will never throw a NPE.