@SuppressWarnings("unchecked")
    public final M returningOld() {
      options.returnDocument(ReturnDocument.BEFORE);
      return (M) this;
    }
Configures this modifier so that old (not updated) version of document will be returned in
case of successful update.
This is default behavior so it may be called only for explanatory reasons.
@see #returningNew()
@return {@code this} modifier for chained invocation
mongo/src/org/immutables/mongo/repository/Repositories.java