code: public Option<V> getMultiple(final K parent, final Selector selector) {
          return Option.of(this.prototypes.get(parent)).map(selectorMap -> selectorMap.get(selector));
      }
docs: Tries to find the instance you look for. Returns an {@link Option} (similar to {@link Optional}) that either
  contains {@link Option.Some} (found) or {@link Option.None} (not found/exception was thrown).
  <p>
  Look at {@link Option} for information on how to use it.
  
  @param parent   The instance who's children you look for.
  @param selector The selector previously used in #registerMultiple(TYPE_COMMON_INST, TYPE_Selector,
  TYPE_ACTUAL_INST).
  
  @return The {@link Option} that either contains it ({@link Option.Some}) or is empty. That is, {@link
  Option.None}, which means that it was not found or at some point in the hierarchy there has been an exception).