code: public PushOptions sortDocument(@Nullable final Bson sortDocument) {
          if (sort != null) {
              throw new IllegalStateException("sortDocument can not be set if sort already is");
          }
          this.sortDocument = sortDocument;
          return this;
      }
docs: Sets the sort direction for sorting array elements that are documents.
  
  @param sortDocument the sort document
  @return this
  @throws IllegalStateException if sort property is already set
  @mongodb.driver.manual reference/operator/update/sort/ $sort