Function parse_labels_param 

pub fn parse_labels_param(
    value: Option<&Value>,
) -> Result<BTreeMap<String, String>, String>

Parse a JSON labels field as a string→string map.

Accepts a missing field, null, or an empty object — all yield an empty map. Anything else must deserialize cleanly or returns a human-readable error string suitable for a JSON-RPC Invalid params reply.