public List<ResolveResult> resolve(ComponentSpecification sourceRef, Properties sourceToProviderMap) {
        ResolveResult searchChainResolveResult = searchChainResolver.resolve(sourceRef, sourceToProviderMap);
        if (searchChainResolveResult.invocationSpec() == null) {
            return resolveClustersWithDocument(sourceRef, sourceToProviderMap);
        }
        return List.of(searchChainResolveResult);
    }
Maps a source reference to search chain invocation specs.

@author Tony Vaagenes
container-search/src/main/java/com/yahoo/search/federation/sourceref/SourceRefResolver.java