diff --git a/backend/src/services/incident.service.ts b/backend/src/services/incident.service.ts
index cb59e20..dcda192 100644
--- a/backend/src/services/incident.service.ts
+++ b/backend/src/services/incident.service.ts
@@ -560,7 +560,7 @@ class IncidentService {
         [targetYear]
       );
 
-      const totals = totalsResult.rows[0];
+      const totals = totalsResult.rows[0] ?? { gesamt: 0, abgeschlossen: 0, aktiv: 0, avg_hilfsfrist_min: null };
 
       // Monthly breakdown — target year
       const monthlyResult = await pool.query(
@@ -636,21 +636,21 @@ class IncidentService {
       const haeufigste_art: EinsatzArt | null =
         byArtResult.rows.length > 0 ? (byArtResult.rows[0].einsatz_art as EinsatzArt) : null;
 
-      const monthly: MonthlyStatRow[] = monthlyResult.rows.map((r) => ({
+      const monthly: MonthlyStatRow[] = (monthlyResult.rows ?? []).map((r) => ({
         monat: r.monat,
         anzahl: r.anzahl,
         avg_hilfsfrist_min: r.avg_hilfsfrist_min !== null ? Number(r.avg_hilfsfrist_min) : null,
         avg_dauer_min: r.avg_dauer_min !== null ? Number(r.avg_dauer_min) : null,
       }));
 
-      const prev_year_monthly: MonthlyStatRow[] = prevMonthlyResult.rows.map((r) => ({
+      const prev_year_monthly: MonthlyStatRow[] = (prevMonthlyResult.rows ?? []).map((r) => ({
         monat: r.monat,
         anzahl: r.anzahl,
         avg_hilfsfrist_min: r.avg_hilfsfrist_min !== null ? Number(r.avg_hilfsfrist_min) : null,
         avg_dauer_min: r.avg_dauer_min !== null ? Number(r.avg_dauer_min) : null,
       }));
 
-      const by_art: EinsatzArtStatRow[] = byArtResult.rows.map((r) => ({
+      const by_art: EinsatzArtStatRow[] = (byArtResult.rows ?? []).map((r) => ({
         einsatz_art: r.einsatz_art as EinsatzArt,
         anzahl: r.anzahl,
         avg_hilfsfrist_min: r.avg_hilfsfrist_min !== null ? Number(r.avg_hilfsfrist_min) : null,
diff --git a/backend/src/services/member.service.ts b/backend/src/services/member.service.ts
index f07bd50..498a99f 100644
--- a/backend/src/services/member.service.ts
+++ b/backend/src/services/member.service.ts
@@ -236,6 +236,8 @@ class MemberService {
       // Attach rank history when the profile exists
       if (member.profile) {
         member.dienstgrad_verlauf = await this.getDienstgradVerlauf(userId);
+      } else {
+        member.dienstgrad_verlauf = [];
       }
 
       return member;
@@ -583,7 +585,15 @@ class MemberService {
         FROM mitglieder_profile
       `);
 
-      return result.rows[0] as MemberStats;
+      return (result.rows[0] as MemberStats) ?? {
+        total: 0,
+        aktiv: 0,
+        passiv: 0,
+        ehrenmitglied: 0,
+        jugendfeuerwehr: 0,
+        'anwärter': 0,
+        ausgetreten: 0,
+      };
     } catch (error) {
       logger.error('Error fetching member stats', { error });
       throw new Error('Failed to fetch member stats');
diff --git a/backend/src/services/vehicle.service.ts b/backend/src/services/vehicle.service.ts
index a02eeb7..b271ff5 100644
--- a/backend/src/services/vehicle.service.ts
+++ b/backend/src/services/vehicle.service.ts
@@ -373,16 +373,16 @@ class VehicleService {
         WHERE deleted_at IS NULL
       `);
 
-      const totals = totalsResult.rows[0];
-      const alerts = alertResult.rows[0];
+      const totals = totalsResult.rows[0] ?? { total: '0', einsatzbereit: '0', ausser_dienst: '0', in_lehrgang: '0' };
+      const alerts = alertResult.rows[0] ?? { inspections_due: '0', inspections_overdue: '0' };
 
       return {
-        total:              parseInt(totals.total, 10),
-        einsatzbereit:      parseInt(totals.einsatzbereit, 10),
-        ausserDienst:       parseInt(totals.ausser_dienst, 10),
-        inLehrgang:         parseInt(totals.in_lehrgang, 10),
-        inspectionsDue:     parseInt(alerts.inspections_due, 10),
-        inspectionsOverdue: parseInt(alerts.inspections_overdue, 10),
+        total:              parseInt(totals.total ?? '0', 10),
+        einsatzbereit:      parseInt(totals.einsatzbereit ?? '0', 10),
+        ausserDienst:       parseInt(totals.ausser_dienst ?? '0', 10),
+        inLehrgang:         parseInt(totals.in_lehrgang ?? '0', 10),
+        inspectionsDue:     parseInt(alerts.inspections_due ?? '0', 10),
+        inspectionsOverdue: parseInt(alerts.inspections_overdue ?? '0', 10),
       };
     } catch (error) {
       logger.error('VehicleService.getVehicleStats failed', { error });
diff --git a/frontend/src/pages/FahrzeugDetail.tsx b/frontend/src/pages/FahrzeugDetail.tsx
index 67e0d3b..9a1b44d 100644
--- a/frontend/src/pages/FahrzeugDetail.tsx
+++ b/frontend/src/pages/FahrzeugDetail.tsx
@@ -14,6 +14,7 @@ import {
   Fab,
   FormControl,
   Grid,
+  IconButton,
   InputLabel,
   MenuItem,
   Paper,
diff --git a/frontend/src/services/incidents.ts b/frontend/src/services/incidents.ts
index 60d7289..177e223 100644
--- a/frontend/src/services/incidents.ts
+++ b/frontend/src/services/incidents.ts
@@ -216,7 +216,7 @@ export const incidentsApi = {
     const response = await api.get<{ success: boolean; data: IncidentListResponse }>(
       `/api/incidents?${params.toString()}`
     );
-    if (!response.data?.data) {
+    if (response.data?.data === undefined || response.data?.data === null) {
       throw new Error('Invalid API response');
     }
     return response.data.data;
@@ -230,7 +230,7 @@ export const incidentsApi = {
     const response = await api.get<{ success: boolean; data: EinsatzStats }>(
       `/api/incidents/stats${params}`
     );
-    if (!response.data?.data) {
+    if (response.data?.data === undefined || response.data?.data === null) {
       throw new Error('Invalid API response');
     }
     return response.data.data;
@@ -243,7 +243,7 @@ export const incidentsApi = {
     const response = await api.get<{ success: boolean; data: EinsatzDetail }>(
       `/api/incidents/${id}`
     );
-    if (!response.data?.data) {
+    if (response.data?.data === undefined || response.data?.data === null) {
       throw new Error('Invalid API response');
     }
     return response.data.data;
@@ -257,7 +257,7 @@ export const incidentsApi = {
       '/api/incidents',
       payload
     );
-    if (!response.data?.data) {
+    if (response.data?.data === undefined || response.data?.data === null) {
       throw new Error('Invalid API response');
     }
     return response.data.data;
@@ -271,7 +271,7 @@ export const incidentsApi = {
       `/api/incidents/${id}`,
       payload
     );
-    if (!response.data?.data) {
+    if (response.data?.data === undefined || response.data?.data === null) {
       throw new Error('Invalid API response');
     }
     return response.data.data;
diff --git a/frontend/src/services/members.ts b/frontend/src/services/members.ts
index 0dab506..0092127 100644
--- a/frontend/src/services/members.ts
+++ b/frontend/src/services/members.ts
@@ -55,7 +55,7 @@ export const membersService = {
     const response = await api.get<ApiListResponse<MemberListItem>>(
       `/api/members?${params.toString()}`
     );
-    if (!response.data?.data) {
+    if (response.data?.data === undefined || response.data?.data === null) {
       throw new Error('Invalid API response');
     }
     return {
@@ -72,7 +72,7 @@ export const membersService = {
     const response = await api.get<ApiItemResponse<MemberWithProfile>>(
       `/api/members/${userId}`
     );
-    if (!response.data?.data) {
+    if (response.data?.data === undefined || response.data?.data === null) {
       throw new Error('Invalid API response');
     }
     return response.data.data;
@@ -90,7 +90,7 @@ export const membersService = {
       `/api/members/${userId}/profile`,
       data
     );
-    if (!response.data?.data) {
+    if (response.data?.data === undefined || response.data?.data === null) {
       throw new Error('Invalid API response');
     }
     return response.data.data;
@@ -109,7 +109,7 @@ export const membersService = {
       `/api/members/${userId}`,
       data
     );
-    if (!response.data?.data) {
+    if (response.data?.data === undefined || response.data?.data === null) {
       throw new Error('Invalid API response');
     }
     return response.data.data;
@@ -120,7 +120,7 @@ export const membersService = {
    */
   async getMemberStats(): Promise<MemberStats> {
     const response = await api.get<ApiItemResponse<MemberStats>>('/api/members/stats');
-    if (!response.data?.data) {
+    if (response.data?.data === undefined || response.data?.data === null) {
       throw new Error('Invalid API response');
     }
     return response.data.data;
diff --git a/frontend/src/services/vehicles.ts b/frontend/src/services/vehicles.ts
index 3604921..b0e15ff 100644
--- a/frontend/src/services/vehicles.ts
+++ b/frontend/src/services/vehicles.ts
@@ -15,7 +15,7 @@ async function unwrap<T>(
   promise: ReturnType<typeof api.get<{ success: boolean; data: T }>>
 ): Promise<T> {
   const response = await promise;
-  if (!response.data?.data) {
+  if (response.data?.data === undefined || response.data?.data === null) {
     throw new Error('Invalid API response');
   }
   return response.data.data;
@@ -47,7 +47,7 @@ export const vehiclesApi = {
       '/api/vehicles',
       payload
     );
-    if (!response.data?.data) {
+    if (response.data?.data === undefined || response.data?.data === null) {
       throw new Error('Invalid API response');
     }
     return response.data.data;
@@ -58,7 +58,7 @@ export const vehiclesApi = {
       `/api/vehicles/${id}`,
       payload
     );
-    if (!response.data?.data) {
+    if (response.data?.data === undefined || response.data?.data === null) {
       throw new Error('Invalid API response');
     }
     return response.data.data;
@@ -83,7 +83,7 @@ export const vehiclesApi = {
       `/api/vehicles/${id}/wartung`,
       payload
     );
-    if (!response.data?.data) {
+    if (response.data?.data === undefined || response.data?.data === null) {
       throw new Error('Invalid API response');
     }
     return response.data.data;