Set<String> removeServiceIfTraceId(String lowTraceId) {
      Set<String> result = new LinkedHashSet<>();
      for (Map.Entry<String, Collection<String>> entry : delegate.entrySet()) {
        Collection<String> lowTraceIds = entry.getValue();
        if (lowTraceIds.remove(lowTraceId) && lowTraceIds.isEmpty()) {
          result.add(entry.getKey());
        }
      }
      delegate.keySet().removeAll(result);
      return result;
    }
Returns service names orphaned by removing the trace ID
zipkin/src/main/java/zipkin2/storage/InMemoryStorage.java