code: public List<ComponentDto> selectDescendants(DbSession dbSession, ComponentTreeQuery query) {
      Optional<ComponentDto> componentOpt = selectByUuid(dbSession, query.getBaseUuid());
      if (!componentOpt.isPresent()) {
        return emptyList();
      }
      ComponentDto component = componentOpt.get();
      return mapper(dbSession).selectDescendants(query, componentOpt.get().uuid(), query.getUuidPath(component));
    }
docs: Select the children or the leaves of a base component, given by its UUID. The components that are not present in last
  analysis are ignored.
  <p>
  An empty list is returned if the base component does not exist or if the base component is a leaf.