test(document): pin undated null->false coercion on /ids (#683)

The /search path already pins the Boolean-undated->primitive coercion via
search_withoutUndatedParam_forwardsFalseToService; add the symmetric pin for
getDocumentIds so an absent param provably resolves to undated=false on the
record (never NPE). Raised in the #702 review.

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

backend/src/test/java/org/raddatz/familienarchiv/document/DocumentControllerTest.java

@@ -1233,6 +1233,24 @@ class DocumentControllerTest {
         assertThat(filtersCaptor.getValue().sender()).isEqualTo(senderId);
     }
 
+    @Test
+    @WithMockUser(authorities = "WRITE_ALL")
+    void getDocumentIds_withoutUndatedParam_coercesNullToFalse() throws Exception {
+        // The controller coerces a null boxed Boolean to primitive false
+        // (Boolean.TRUE.equals(undated)) so the absent param never NPEs and the
+        // record always holds a concrete boolean.
+        when(userService.findByEmail(any())).thenReturn(AppUser.builder().id(UUID.randomUUID()).build());
+        ArgumentCaptor<SearchFilters> filtersCaptor = ArgumentCaptor.forClass(SearchFilters.class);
+        when(documentService.findIdsForFilter(any()))
+                .thenReturn(List.of());
+
+        mockMvc.perform(get("/api/documents/ids"))
+                .andExpect(status().isOk());
+
+        verify(documentService).findIdsForFilter(filtersCaptor.capture());
+        assertThat(filtersCaptor.getValue().undated()).isFalse();
+    }
+
     @Test
     @WithMockUser(authorities = "WRITE_ALL")
     void getDocumentIds_returns400_whenResultExceedsFilterCap() throws Exception {