What happened?

A span from HotROD stored in Elasticsearch fails to load properly. The UI shows:

blockers | invalid string type in [2804-5]

Steps to reproduce

I added logging of a collection-typed attribute to HotROD

diff --git a/examples/hotrod/pkg/tracing/mutex.go b/examples/hotrod/pkg/tracing/mutex.go
index f094d057..7264e995 100644
--- a/examples/hotrod/pkg/tracing/mutex.go
+++ b/examples/hotrod/pkg/tracing/mutex.go
@@ -42,6 +42,7 @@ func (sm *Mutex) Lock(ctx context.Context) {
                        fmt.Sprintf("Waiting for lock behind %d transactions", waiting),
                        zap.String("blockers", fmt.Sprintf("%v", sm.waiters)),
                )
+               activeSpan.SetAttributes(attribute.StringSlice("blockers", sm.waiters))
        }
        sm.waiters = append(sm.waiters, session)
        sm.waitersLock.Unlock()

Run Jaeger with Elasticsearch and HotROD

$ cd docker-compose/elasticsearch/v8
$ docker compose up

$ go run ./cmd/jaeger --config ./cmd/jaeger/config-elasticsearch.yaml

$ go run ./examples/hotrod all

Open HotROD at http://0.0.0.0:8080/ and quickly click one button several times so that latency goes up (blocking in the code). Open the trace and expand tags of the mysql span.

Expected behavior

I expect no errors in the display. The collection-typed tag blockers should be converted into a JSON string.

Relevant log output

The trace can be loaded from Elasticsearch directly (fix index name and trace id):

$ curl -X GET "localhost:9200/jaeger-main-jaeger-span-2025-07-19/_search?pretty" -H 'Content-Type: application/json' -d'
{
  "size": 100,
  "query": {
    "match": {
      "traceID": "b9f674a5dd0395ac04c4f209d93cef07"
    }
  }
}
' > trage.json

It appears to be stored as proper JSON array, but with incorrect type string, which later fails to load.

            {
              "key" : "blockers",
              "type" : "string",
              "value" : [
                "2804-5"
              ]
            }