From fd06fbbb5d2ca49388a6de89625060df262b2eb9 Mon Sep 17 00:00:00 2001
From: Daniel Noulet <daniel.noulet@gmail.com>
Date: Sat, 19 Sep 2026 21:34:12 +0200
Subject: [PATCH] fix: handle empty candidate trait lists

Return empty JSON arrays from the API and normalize nullable values from older servers before rendering candidate match counts.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 backend/internal/web/mapper/mapper.go      | 10 +++++++++-
 backend/internal/web/mapper/mapper_test.go |  7 +++++++
 frontend/src/App.test.tsx                  | 13 ++++++++++++-
 frontend/src/api.ts                        |  9 ++++++++-
 4 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/backend/internal/web/mapper/mapper.go b/backend/internal/web/mapper/mapper.go
index 803ae27..67fad0e 100644
--- a/backend/internal/web/mapper/mapper.go
+++ b/backend/internal/web/mapper/mapper.go
@@ -66,9 +66,17 @@ func ParticipantToWeb(value servicemodel.Participant) webmodel.ParticipantRespon
 }
 
 func CandidateToWeb(value servicemodel.CandidateMatch) webmodel.CandidateResponse {
+	matched := value.Matched
+	if matched == nil {
+		matched = []string{}
+	}
+	missing := value.Missing
+	if missing == nil {
+		missing = []string{}
+	}
 	return webmodel.CandidateResponse{
 		Participant: ParticipantToWeb(value.Participant), Score: value.Score,
-		Matched: value.Matched, Missing: value.Missing,
+		Matched: matched, Missing: missing,
 	}
 }
 
diff --git a/backend/internal/web/mapper/mapper_test.go b/backend/internal/web/mapper/mapper_test.go
index d25d429..0c1b70a 100644
--- a/backend/internal/web/mapper/mapper_test.go
+++ b/backend/internal/web/mapper/mapper_test.go
@@ -19,3 +19,10 @@ func TestInterviewOmitsReferenceAnswer(t *testing.T) {
 		t.Fatalf("expected participant-safe code question, got %#v", response)
 	}
 }
+
+func TestCandidateAlwaysUsesJSONArrays(t *testing.T) {
+	response := CandidateToWeb(servicemodel.CandidateMatch{})
+	if response.Matched == nil || response.Missing == nil {
+		t.Fatalf("candidate trait collections must not be nil: %#v", response)
+	}
+}
diff --git a/frontend/src/App.test.tsx b/frontend/src/App.test.tsx
index 682bc54..59b0037 100644
--- a/frontend/src/App.test.tsx
+++ b/frontend/src/App.test.tsx
@@ -69,7 +69,7 @@ function mockApi() {
             participant,
             score: 90,
             matchedTraits: ['Go'],
-            missingTraits: [],
+            missingTraits: null,
           },
         ])
       if (path === '/api/jobs/7/invitations' && method === 'GET') return response([])
@@ -129,6 +129,17 @@ describe('Go Guess frontend', () => {
     mockApi()
   })
 
+  it('renders candidate matches when an older API returns null trait arrays', async () => {
+    authenticate()
+    const user = userEvent.setup()
+    renderApp('/jobs/7')
+
+    await user.click(await screen.findByRole('tab', { name: /candidate match/i }))
+
+    expect(await screen.findByText('90%')).toBeInTheDocument()
+    expect(screen.getByText('Missing').nextElementSibling).toHaveTextContent('0')
+  })
+
   it('persists login, navigates from the login URL, and shows API jobs', async () => {
     const user = userEvent.setup()
     window.history.replaceState({}, '', '/login')
diff --git a/frontend/src/api.ts b/frontend/src/api.ts
index f613e2f..e8dcdae 100644
--- a/frontend/src/api.ts
+++ b/frontend/src/api.ts
@@ -115,7 +115,14 @@ export const api = {
       }),
     detachQuestion: (jobId: number, questionId: number) =>
       request<void>(`/jobs/${jobId}/questions/${questionId}`, { method: 'DELETE' }),
-    candidates: (jobId: number) => request<CandidateMatch[]>(`/jobs/${jobId}/candidates`),
+    candidates: async (jobId: number) => {
+      const matches = await request<CandidateMatch[]>(`/jobs/${jobId}/candidates`)
+      return matches.map((match) => ({
+        ...match,
+        matchedTraits: match.matchedTraits ?? [],
+        missingTraits: match.missingTraits ?? [],
+      }))
+    },
     invitations: (jobId: number) => request<Invitation[]>(`/jobs/${jobId}/invitations`),
     invitation: (jobId: number, invitationId: number) =>
       request<Interview>(`/jobs/${jobId}/invitations/${invitationId}`),