These work

server-rs/src/routes/postcode_stats.rs

@@ -52,7 +52,8 @@ pub async fn get_postcode_stats(
         params.filters.as_deref(),
         &state.feature_name_to_index,
         &state.data.enum_values,
-    );
+    )
+    .map_err(|err| (StatusCode::BAD_REQUEST, err))?;
     let num_filters = parsed_filters.len() + parsed_enum_filters.len();
 
     let (fields_specified, field_set) = parse_field_set(params.fields.as_deref());