code: public Optional<Integer> getInteger(String key) {
      return this.get(key).map(Integer::valueOf);
    }
docs: Gets the flag value for the given key as an Integer, wrapped in an {@link Optional}, which is
  empty if the flag is unset.
  
  <p>If the flag's value cannot be interpreted as an Integer, throws a {@link
  NumberFormatException} (note: float values will *not* be interpreted as integers and will throw
  an exception!)