code: public EntityBuilder addSubEntities(List<Entity> entities) {
      	if(entities == null) {
      		throw new IllegalArgumentException("entities cannot be null.");
      	}
      	for (Entity entity : entities) {
              addSubEntity(entity);
          }
          return this;
      }
docs: Add a list of sub entities to the entity to be built.
  Sub entities are optional according to the Siren specification.
  @param entities cannot be <code>null</code>, may be empty.
  @return <code>this</code> builder, never <code>null</code>.