code: @Nonnull
    public Query startAt(Object... fieldValues) {
      QueryOptions newOptions = new QueryOptions(options);
      newOptions.startCursor = createCursor(newOptions.fieldOrders, fieldValues, true);
      return new Query(firestore, path, newOptions);
    }
docs: Creates and returns a new Query that starts at the provided fields relative to the order of the
  query. The order of the field values must match the order of the order by clauses of the query.
  
  @param fieldValues The field values to start this query at, in order of the query's order by.
  @return The created Query.