Why I met the error 'called Result::unwrap() on an Err value: Error { kind: ToSql(2), cause: Some(WrongType { postgres: Json, rust: "core::option::Option<alloc::string::String>" }) }' when I sent 'POST /v1/conversations' request

[tianzhiqiang3]

• version: sglang-model-gateway v0.2.4
• environment: kubernetes v1.30.12
• image: lmsysorg/sglang-router:v0.2.4
• start command: python3 -m sglang_router.launch_router --service-discovery --policy random --service-discovery-port 30000 --selector storm-service-name=ds-distill-qwen3-8b-s5ahrc --service-discovery-namespace model-evaluate --history-backend postgres --postgres-db-url postgres://postgres:******@172.31.0.181:5432/sglang-router --host 0.0.0.0 --port 8080
• issue: I have deployed a pod named sglang-router, and exposed by http://172.30.3.79:8080. When I executed this command curl -X POST "http://172.30.3.79:8080/v1/conversations" -H "Content-Type: application/json" --data '{"metadata":{"foo":"bar"}}', I got Empty reply from server. And I check the logs of sglang-router, I got this error

thread 'tokio-runtime-worker' (23) panicked at /opt/sglang/sgl-model-gateway/src/data_connector/postgres.rs:127:14:
called `Result::unwrap()` on an `Err` value: Error { kind: ToSql(2), cause: Some(WrongType { postgres: Json, rust: "core::option::Option<alloc::string::String>" }) }

Something strange is, after I update the type of field metadata of conversations table from 'json' to 'text', the curl command executed successfully and data was inserted.
So why I met this issue? Is this a bug?