Return null instead of undefined on 404 in conformance trace detail methods

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/stores/conformance.ts

@@ -347,7 +347,7 @@ export const useConformanceStore = defineStore("conformanceStore", {
       } catch (error) {
         if (error.response?.status === 404) {
           this.infinite404 = 404;
-          return;
+          return null;
         }
         apiError(
           error,
@@ -387,7 +387,7 @@ export const useConformanceStore = defineStore("conformanceStore", {
       } catch (error) {
         if (error.response?.status === 404) {
           this.infinite404 = 404;
-          return;
+          return null;
         }
         apiError(
           error,