Handle null prefer in inline routing policy (#856)

* Handle null prefer in inline routing policy

* Use serde defaulting for null selection preference

* Add tests for default selection policy behavior in routing preferences

crates/brightstaff/src/handlers/routing_service.rs

@@ -197,6 +197,7 @@ async fn routing_decision_inner(
 #[cfg(test)]
 mod tests {
     use super::*;
+    use common::configuration::SelectionPreference;
 
     fn make_chat_body(extra_fields: &str) -> Vec<u8> {
         let extra = if extra_fields.is_empty() {
@@ -264,6 +265,61 @@ mod tests {
         assert!(cleaned_json.get("routing_preferences").is_none());
     }
 
+    #[test]
+    fn extract_routing_policy_prefer_null_defaults_to_none() {
+        let policy = r#""routing_preferences": [
+            {
+                "name": "coding",
+                "description": "code generation, writing functions, debugging",
+                "models": ["openai/gpt-4o", "openai/gpt-4o-mini"],
+                "selection_policy": {"prefer": null}
+            }
+        ]"#;
+        let body = make_chat_body(policy);
+        let (_cleaned, prefs) = extract_routing_policy(&body).unwrap();
+
+        let prefs = prefs.expect("should parse routing_preferences when prefer is null");
+        assert_eq!(prefs.len(), 1);
+        assert_eq!(prefs[0].selection_policy.prefer, SelectionPreference::None);
+    }
+
+    #[test]
+    fn extract_routing_policy_selection_policy_missing_defaults_to_none() {
+        let policy = r#""routing_preferences": [
+            {
+                "name": "coding",
+                "description": "code generation, writing functions, debugging",
+                "models": ["openai/gpt-4o", "openai/gpt-4o-mini"]
+            }
+        ]"#;
+        let body = make_chat_body(policy);
+        let (_cleaned, prefs) = extract_routing_policy(&body).unwrap();
+
+        let prefs =
+            prefs.expect("should parse routing_preferences when selection_policy is missing");
+        assert_eq!(prefs.len(), 1);
+        assert_eq!(prefs[0].selection_policy.prefer, SelectionPreference::None);
+    }
+
+    #[test]
+    fn extract_routing_policy_prefer_empty_string_defaults_to_none() {
+        let policy = r#""routing_preferences": [
+            {
+                "name": "coding",
+                "description": "code generation, writing functions, debugging",
+                "models": ["openai/gpt-4o", "openai/gpt-4o-mini"],
+                "selection_policy": {"prefer": ""}
+            }
+        ]"#;
+        let body = make_chat_body(policy);
+        let (_cleaned, prefs) = extract_routing_policy(&body).unwrap();
+
+        let prefs =
+            prefs.expect("should parse routing_preferences when selection_policy.prefer is empty");
+        assert_eq!(prefs.len(), 1);
+        assert_eq!(prefs[0].selection_policy.prefer, SelectionPreference::None);
+    }
+
     #[test]
     fn routing_decision_response_serialization() {
         let response = RoutingDecisionResponse {

crates/common/src/configuration.rs

@@ -1,5 +1,5 @@
 use hermesllm::apis::openai::{ModelDetail, ModelObject, Models};
-use serde::{Deserialize, Serialize};
+use serde::{Deserialize, Deserializer, Serialize};
 use std::collections::HashMap;
 use std::fmt::Display;
 
@@ -111,14 +111,25 @@ pub enum SelectionPreference {
     Fastest,
     /// Return models in the same order they were defined — no reordering.
     #[default]
+    #[serde(alias = "")]
     None,
 }
 
 #[derive(Debug, Clone, Default, Serialize, Deserialize)]
 pub struct SelectionPolicy {
+    #[serde(default, deserialize_with = "deserialize_selection_preference")]
     pub prefer: SelectionPreference,
 }
 
+fn deserialize_selection_preference<'de, D>(
+    deserializer: D,
+) -> Result<SelectionPreference, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    Ok(Option::<SelectionPreference>::deserialize(deserializer)?.unwrap_or_default())
+}
+
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct TopLevelRoutingPreference {
     pub name: String,