code: public List<IssueDto> selectByKeys(DbSession session, Collection<String> keys) {
      return executeLargeInputs(keys, mapper(session)::selectByKeys);
    }
docs: Gets a list issues by their keys. The result does NOT contain {@code null} values for issues not found, so
  the size of result may be less than the number of keys. A single issue is returned
  if input keys contain multiple occurrences of a key.
  <p>Results may be in a different order as input keys.</p>