code: @InterfaceAudience.Public
      public boolean isDeletion() {
          Object deleted = getProperty("_deleted");
          if (deleted == null) {
              return false;
          }
          Boolean deletedBool = (Boolean) deleted;
          return deletedBool.booleanValue();
      }
docs: Does this revision mark the deletion of its document?
  (In other words, does it have a "_deleted" property?)