code: public List<Entry> storeSkipExisting(List<Entry> entries) throws MissingParentException {
          List<Entry> skippedEntries = new LinkedList<Entry>();
          for (Entry e : entries) {
              try {
                  store(e);
              } catch (EntryAlreadyExistsException ex) {
                  skippedEntries.add(e);
              }
          }
          return skippedEntries;
      }
docs: Behaves like {@link #store(List)} except that duplicates do not throw an exception but are collected in a list
  which will be returned at success. Note that this action is not atomic.