private static <T> Set<T> immutableCopy(Set<T> set) {
        if (set == null) return ImmutableSet.of();
        return ImmutableSet.copyOf(set);
    }
@param allChainSpecifications resolves ChainSpecifications from ComponentSpecifications
                              as given in the inheritance fields.
@param path tracks which chains are used in each recursive invocation of flatten, used for detecting cycles.
@return ChainSpecification directly containing all the component references and phases of the inherited chains.
container-core/src/main/java/com/yahoo/component/chain/model/ChainSpecification.java