@Override
      public @NotNull Collection<V> createValue(K key) {
        try {
          final Collection<V> collection = myMap.get(key);
          //noinspection unchecked
          return collection == null? (Collection<V>)NULL_COLLECTION : collection;
        }
        catch (IOException e) {
          throw new BuildDataCorruptedException(e);
        }
      }
@Override
      public @NotNull Collection<V> createValue(K key)