fix(dashboard): null-safe name join in toActorDTO

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

backend/src/test/java/org/raddatz/familienarchiv/dashboard/DashboardServiceTest.java

@@ -0,0 +1,68 @@
+package org.raddatz.familienarchiv.dashboard;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.InjectMocks;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+import org.raddatz.familienarchiv.model.AppUser;
+import org.raddatz.familienarchiv.model.Document;
+import org.raddatz.familienarchiv.model.TranscriptionBlock;
+import org.raddatz.familienarchiv.service.DocumentService;
+import org.raddatz.familienarchiv.service.TranscriptionService;
+import org.raddatz.familienarchiv.service.UserService;
+
+import java.time.LocalDateTime;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Optional;
+import java.util.UUID;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.when;
+
+@ExtendWith(MockitoExtension.class)
+class DashboardServiceTest {
+
+    @Mock AuditLogQueryService auditLogQueryService;
+    @Mock DocumentService documentService;
+    @Mock TranscriptionService transcriptionService;
+    @Mock UserService userService;
+
+    @InjectMocks DashboardService dashboardService;
+
+    // ─── toActorDTO (via getResume collaborators) ─────────────────────────────
+
+    @Test
+    void getResume_collaboratorName_isNullSafe_whenFirstNameIsNull() {
+        UUID userId = UUID.randomUUID();
+        UUID docId = UUID.randomUUID();
+        UUID collaboratorId = UUID.randomUUID();
+
+        Document doc = Document.builder()
+                .id(docId).title("Brief").originalFilename("brief.pdf")
+                .receivers(new HashSet<>())
+                .build();
+
+        TranscriptionBlock block = TranscriptionBlock.builder()
+                .id(UUID.randomUUID()).annotationId(UUID.randomUUID())
+                .documentId(docId).sortOrder(1).updatedBy(collaboratorId)
+                .build();
+
+        AppUser collaborator = AppUser.builder()
+                .id(collaboratorId).email("s@test.com").password("pw")
+                .firstName(null).lastName("Schmidt").color("#abc")
+                .build();
+
+        when(auditLogQueryService.findMostRecentDocumentForUser(userId)).thenReturn(Optional.of(docId));
+        when(documentService.getDocumentById(docId)).thenReturn(doc);
+        when(transcriptionService.listBlocks(docId)).thenReturn(List.of(block));
+        when(userService.getById(collaboratorId)).thenReturn(collaborator);
+
+        DashboardResumeDTO result = dashboardService.getResume(userId);
+
+        assertThat(result).isNotNull();
+        assertThat(result.collaborators()).hasSize(1);
+        assertThat(result.collaborators().get(0).name()).isEqualTo("Schmidt");
+    }
+}