docs: public DocumentOperationResults performOnEachDocument( BiFunction<String, EditableDocument, Boolean> operation ) {
          DocumentOperationResults results = new DocumentOperationResults();
          database.keys().forEach(key -> 
              runInTransaction(() -> {
                  // We operate upon each document within a transaction ...
                  try {
                      EditableDocument doc = edit(key, false);
                      if (doc != null) {
                          if (operation.apply(key, doc)) {
                              results.recordModified();
                          } else {
                              results.recordUnmodified();
                          }
                      }
                  } catch (Throwable t) {
                      results.recordFailure();
                  }
                  return null;
              }, 1, key));
          return results;
      }