diff --git a/frontend/src/asset_manager.ts b/frontend/src/asset_manager.ts
index 94f030a..7692cc7 100644
--- a/frontend/src/asset_manager.ts
+++ b/frontend/src/asset_manager.ts
@@ -2,6 +2,8 @@ import type { AxiosInstance } from 'axios';
 
 export type Identifier = string | number;
 
+type Nullable<T> = T | null;
+
 export interface AssetObject {
   ordinal?: number;
   url?: string | null;
@@ -40,12 +42,12 @@ export type EnsureAssetUrl = (
   options?: { start?: number | null; limit?: number | null; force?: boolean; [key: string]: unknown },
 ) => Promise<unknown>;
 
-export type GetAsset = (document: DocumentLike, assetType: string) => AssetLike | null | undefined;
+export type GetAsset = (document: DocumentLike, assetType: string) => Nullable<AssetLike>;
 
 export const getAssetFromGroup = (
-  assets: AssetLike[] | Record<string, AssetLike> | null | undefined,
-  assetType: string,
-): AssetLike | null => {
+  assets?: AssetLike[] | Record<string, AssetLike> | null,
+  assetType: string = '',
+): Nullable<AssetLike> => {
   if (!assetType || !assets) {
     return null;
   }
@@ -57,11 +59,11 @@ export const getAssetFromGroup = (
   return assets?.[assetType] || null;
 };
 
-export const getAssetFromVersion = (currentVersion, assetType) => {
+export const getAssetFromVersion = (currentVersion: Nullable<DocumentVersionLike>, assetType: string) => {
   if (!currentVersion) {
     return null;
   }
-  return getAssetFromGroup(currentVersion.assets, assetType);
+  return getAssetFromGroup(currentVersion.assets ?? null, assetType);
 };
 
 const normalizeAssetObjects = (objects?: AssetObject[] | null): AssetObject[] => {
@@ -182,7 +184,7 @@ export class AssetView {
 export const createAssetView = (asset?: AssetLike | null): AssetView => new AssetView(asset);
 
 export const resolveDocumentAssetUrl = (
-  doc: DocumentLike | null | undefined,
+  doc: Nullable<DocumentLike>,
   type: string,
   {
     ensureAssetUrl,
@@ -195,7 +197,7 @@ export const resolveDocumentAssetUrl = (
     ensureOptions?: { start?: number; limit?: number; [key: string]: unknown };
     objectOrdinal?: number;
   } = {},
-): string | null => {
+): Nullable<string> => {
   if (!doc || !type) {
     return null;
   }
@@ -251,13 +253,13 @@ class AssetManager {
     this.api = api;
   }
 
-  rememberAsset(entry: AssetLike | null | undefined) {
+  rememberAsset(entry?: Nullable<AssetLike>) {
     if (entry?.id) {
       this.assetCache.set(entry.id, entry);
     }
   }
 
-  hydrateAsset(asset: AssetLike | null | undefined): AssetLike | null | undefined {
+  hydrateAsset(asset?: Nullable<AssetLike>): Nullable<AssetLike> {
     if (!asset || !asset.id) {
       return asset;
     }
@@ -287,7 +289,7 @@ class AssetManager {
     return merged;
   }
 
-  hydrateDocument(document: DocumentLike | null | undefined): DocumentLike | null | undefined {
+  hydrateDocument(document?: Nullable<DocumentLike>): Nullable<DocumentLike> {
     if (!document) {
       return document;
     }
@@ -330,14 +332,14 @@ class AssetManager {
     return { ...document, current_version: nextCurrentVersion };
   }
 
-  hydrateDocuments(documents: DocumentLike[] | null | undefined) {
+  hydrateDocuments(documents?: DocumentLike[] | null) {
     if (!Array.isArray(documents)) {
-      return documents;
+      return documents ?? [];
     }
     return documents.map((doc) => this.hydrateDocument(doc));
   }
 
-  hydrateDetail(detail: { document?: DocumentLike; assets?: AssetLike[] } | null | undefined) {
+  hydrateDetail(detail?: { document?: DocumentLike; assets?: AssetLike[] } | null) {
     if (!detail) {
       return detail;
     }
@@ -366,10 +368,7 @@ class AssetManager {
     return changed ? next : detail;
   }
 
-  hydrateFolderContents(contents: {
-    documents?: DocumentLike[];
-    document?: DocumentLike;
-  } | null | undefined) {
+  hydrateFolderContents(contents?: { documents?: DocumentLike[]; document?: DocumentLike } | null) {
     if (!contents) {
       return contents;
     }
@@ -384,12 +383,12 @@ class AssetManager {
   }
 
   ensureAsset(
-    documentId: Identifier | null | undefined,
-    asset: AssetLike | null | undefined,
+    documentId?: Identifier | null,
+    asset?: Nullable<AssetLike>,
     { force = false, start = null, limit = null }: { force?: boolean; start?: number | null; limit?: number | null } = {},
-  ): Promise<AssetLike | null> {
+  ): Promise<Nullable<AssetLike>> {
     if (!documentId || !asset?.id) {
-      return Promise.resolve(asset || null);
+      return Promise.resolve(asset ?? null);
     }
 
     const requestedStart = Number.isInteger(start) && start > 0 ? start : 1;
diff --git a/frontend/src/documents/DocumentSummarySection.tsx b/frontend/src/documents/DocumentSummarySection.tsx
index 7d6410d..ef7509f 100644
--- a/frontend/src/documents/DocumentSummarySection.tsx
+++ b/frontend/src/documents/DocumentSummarySection.tsx
@@ -476,7 +476,7 @@ const DocumentSummarySection: React.FC<DocumentSummarySectionProps> = ({
   }, [correspondents, document?.correspondents]);
 
   const metaRows = useMemo(() => {
-    const rows: { key: string; label: string; value: string | null | undefined }[] = [];
+    const rows: { key: string; label: string; value: string | null }[] = [];
     const currentVersionNumber = document?.current_version?.version_number;
     if (Number.isFinite(currentVersionNumber)) {
       rows.push({
diff --git a/frontend/src/documents/DocumentThumbnailImage.tsx b/frontend/src/documents/DocumentThumbnailImage.tsx
index 38681a1..1e0679b 100644
--- a/frontend/src/documents/DocumentThumbnailImage.tsx
+++ b/frontend/src/documents/DocumentThumbnailImage.tsx
@@ -17,7 +17,7 @@ const DEFAULT_THUMBNAIL_SIZE = 48;
 // Detect when an element becomes visible within a scroll container so we can delay loading.
 const useLazyVisibility = (
   rootRef: MutableRefObject<Element | null> | null,
-  resetKey: string | number | null | undefined,
+  resetKey?: string | number | null,
 ) => {
   const targetRef = useRef<HTMLDivElement | null>(null);
   const [isVisible, setIsVisible] = useState(false);
@@ -66,10 +66,10 @@ const useLazyVisibility = (
   return { ref: targetRef, isVisible };
 };
 
-const getPageCount = (doc: DocumentLike | null | undefined) =>
-  Number.isFinite(doc?.current_version?.metadata?.page_count)
-    ? (doc?.current_version?.metadata?.page_count as number)
-    : null;
+const getPageCount = (doc?: DocumentLike | null) => {
+  const count = doc?.current_version?.metadata?.page_count;
+  return Number.isFinite(count) ? Number(count) : null;
+};
 
 type DocumentLike = AssetManagerDocumentLike;
 type AssetLike = AssetManagerAssetLike;
diff --git a/frontend/src/documents/DocumentsGrid.tsx b/frontend/src/documents/DocumentsGrid.tsx
index 30ab662..4def7a1 100644
--- a/frontend/src/documents/DocumentsGrid.tsx
+++ b/frontend/src/documents/DocumentsGrid.tsx
@@ -80,7 +80,7 @@ interface DocumentsGridProps {
   onTagClick?: (tagId?: Identifier | null) => void;
   scrollRef?: RefObject<HTMLElement | null>;
   onCorrespondentClick?: (correspondentId?: Identifier | null) => void;
-  activeCorrespondentIdSet?: Set<Identifier | null | undefined> | null;
+  activeCorrespondentIdSet?: Set<Identifier | null> | null;
   onDocumentRename?: (docId: Identifier, title: string) => Promise<boolean> | boolean;
 }
 
diff --git a/frontend/src/documents/DocumentsList.tsx b/frontend/src/documents/DocumentsList.tsx
index 7bd09df..9898c29 100644
--- a/frontend/src/documents/DocumentsList.tsx
+++ b/frontend/src/documents/DocumentsList.tsx
@@ -84,7 +84,7 @@ export interface DocumentsListProps {
   tagLookupById?: Map<Identifier, DocumentTag> | null;
   onTagClick?: (tagId?: Identifier | null) => void;
   onCorrespondentClick?: (correspondentId?: Identifier | null) => void;
-  activeCorrespondentIdSet?: Set<Identifier | null | undefined> | null;
+  activeCorrespondentIdSet?: Set<Identifier | null> | null;
   scrollRef?: RefObject<HTMLElement | null>;
 }
 
diff --git a/frontend/src/documents/SelectionFloatingActions.tsx b/frontend/src/documents/SelectionFloatingActions.tsx
index 7dd97a6..c0b9ea6 100644
--- a/frontend/src/documents/SelectionFloatingActions.tsx
+++ b/frontend/src/documents/SelectionFloatingActions.tsx
@@ -16,9 +16,9 @@ import { useWorkspaceSelectionContext } from '../app/WorkspaceSelectionContext';
 const ROOT_FOLDER_LABEL = 'Documents';
 
 type DocumentId = string | number;
-type NullableDocumentId = DocumentId | null | undefined;
+type NullableDocumentId = DocumentId | null;
 
-type SelectedIdList = Array<NullableDocumentId> | null | undefined;
+type SelectedIdList = NullableDocumentId[] | null;
 
 type FolderTreeNode = {
   id?: DocumentId;
@@ -137,8 +137,8 @@ const buildFolderTreeOptions = (tree?: FolderTreeNode[] | null): SelectionAssign
 
 const buildTagAssignments = (
   selectedDocuments: DocumentLike[],
-  tagLookupById: Map<DocumentId, TagOption> | null | undefined,
-  tags: TagOption[] | null | undefined,
+  tagLookupById: Map<DocumentId, TagOption> | null,
+  tags: TagOption[] | null,
   total: number,
 ): SelectionAssignmentMenuItem[] => {
   if (!total) {
@@ -202,7 +202,7 @@ const buildTagAssignments = (
 
 const buildCorrespondentAssignments = (
   selectedDocuments: DocumentLike[],
-  correspondents: CorrespondentOption[] | null | undefined,
+  correspondents: CorrespondentOption[] | null,
   total: number,
 ): SelectionAssignmentMenuItem[] => {
   if (!total) {
@@ -493,7 +493,7 @@ const SelectionFloatingActions: React.FC<SelectionFloatingActionsProps> = ({
       if (!documentIdList.length || !onMoveDocumentsToFolder) {
         return;
       }
-      const candidate = option as { id?: DocumentId; value?: DocumentId } | DocumentId | null | undefined;
+      const candidate = option as { id?: DocumentId; value?: DocumentId } | DocumentId | null;
       const value = isRecord(candidate)
         ? (candidate?.id ?? candidate?.value ?? null)
         : candidate;
diff --git a/frontend/src/documents/documentMetadata.ts b/frontend/src/documents/documentMetadata.ts
index c11b3a7..8f3a32c 100644
--- a/frontend/src/documents/documentMetadata.ts
+++ b/frontend/src/documents/documentMetadata.ts
@@ -20,7 +20,7 @@ export interface DocumentLike {
 
 export interface DocumentMetadataItem {
   label: string;
-  value: string | null | undefined;
+  value: string | null;
 }
 
 export const buildDocumentMetadataItems = (document?: DocumentLike | null): DocumentMetadataItem[] => {
@@ -35,19 +35,19 @@ export const buildDocumentMetadataItems = (document?: DocumentLike | null): Docu
     { label: 'Updated at', value: formatDateTime(document.updated_at) },
     {
       label: 'Filename',
-      value: document.filename,
+      value: document.filename ?? null,
     },
     {
       label: 'Original filename',
-      value: document.original_name || '—',
+      value: document.original_name ?? null,
     },
     {
       label: 'SHA-256 checksum',
-      value: metadata.checksum || '—',
+      value: metadata.checksum ?? null,
     },
     {
       label: 'Content type',
-      value: document.content_type || '—',
+      value: document.content_type ?? null,
     },
   ];
 };
diff --git a/frontend/src/documents/documentSummary.ts b/frontend/src/documents/documentSummary.ts
index 63414be..b9ba845 100644
--- a/frontend/src/documents/documentSummary.ts
+++ b/frontend/src/documents/documentSummary.ts
@@ -38,12 +38,12 @@ interface DescribeSummaryOptions {
 export interface DocumentSummaryRow {
   key: string;
   label: string;
-  value: string | null | undefined;
+  value: string | null;
 }
 
 export interface DocumentSummary {
   title: string | undefined;
-  originalName: string | null | undefined;
+  originalName: string | null;
   mimeTypeLabel: string;
   sizeLabel: string;
   createdAtLabel: string;
@@ -51,7 +51,7 @@ export interface DocumentSummary {
   updatedAtLabel: string;
   pageCount: number | null;
   pageCountLabel: string;
-  folderLabel: string | null | undefined;
+  folderLabel: string | null;
   tags: TagEntry[];
   correspondents: CorrespondentEntry[];
   tagsSummary: string;
@@ -59,7 +59,7 @@ export interface DocumentSummary {
   summaryRows: DocumentSummaryRow[];
 }
 
-const coercePageCount = (metadata: DocumentMetadata | null | undefined): number | null => {
+const coercePageCount = (metadata?: DocumentMetadata | null): number | null => {
   const raw = metadata?.page_count;
   if (raw == null || raw === '') {
     return null;
@@ -68,7 +68,7 @@ const coercePageCount = (metadata: DocumentMetadata | null | undefined): number
   return Number.isFinite(parsed) && parsed >= 0 ? parsed : null;
 };
 
-const sanitizeArray = <T>(entries: (T | null | undefined)[] | null | undefined): T[] =>
+const sanitizeArray = <T>(entries?: Array<T | null> | null): T[] =>
   Array.isArray(entries) ? entries.filter(Boolean) as T[] : [];
 
 export const describeDocumentSummary = (document?: SummaryDocument | null, options: DescribeSummaryOptions = {}): DocumentSummary => {
@@ -79,7 +79,7 @@ export const describeDocumentSummary = (document?: SummaryDocument | null, optio
   if (!document) {
     return {
       title: '',
-      originalName: '',
+      originalName: null,
       mimeTypeLabel: '—',
       sizeLabel: '—',
       createdAtLabel: '—',
@@ -110,7 +110,8 @@ export const describeDocumentSummary = (document?: SummaryDocument | null, optio
   const issuedLabel = formatDateTime(document.issued_at);
   const updatedAtLabel = formatDateTime(document.updated_at);
 
-  const folderLabel = document.folder_path;
+  const folderLabel = document.folder_path ?? null;
+  const displayFolderLabel = folderLabel ?? 'Documents';
 
   const tags = sanitizeArray<TagEntry>(document.tags);
   const correspondents = sanitizeArray<CorrespondentEntry>(document.correspondents);
@@ -130,7 +131,7 @@ export const describeDocumentSummary = (document?: SummaryDocument | null, optio
     { key: 'issued', label: 'Issued', value: issuedLabel },
     { key: 'pages', label: 'Pages', value: pageCountLabel },
     { key: 'updated', label: 'Updated', value: updatedAtLabel },
-    { key: 'folder', label: 'Folder', value: folderLabel },
+    { key: 'folder', label: 'Folder', value: displayFolderLabel },
     { key: 'tags', label: 'Tags', value: tagsSummary },
     { key: 'correspondents', label: 'Correspondents', value: correspondentsSummary },
   ];
diff --git a/frontend/src/documents/tagTransfer.ts b/frontend/src/documents/tagTransfer.ts
index be9813b..9555ebd 100644
--- a/frontend/src/documents/tagTransfer.ts
+++ b/frontend/src/documents/tagTransfer.ts
@@ -21,7 +21,7 @@ const serializePayload = (payload: TagPayload): string | null => {
   }
 };
 
-export const createTagTransferPayload = (tag: TagLike | null | undefined, sourceDocId: string | number | null = null): TagPayload | null => {
+export const createTagTransferPayload = (tag?: TagLike | null, sourceDocId: string | number | null = null): TagPayload | null => {
   if (!tag || tag.id == null) {
     return null;
   }
@@ -58,7 +58,7 @@ export const writeTagTransferData = (dataTransfer: DataTransfer | null, tag: Tag
   }
 };
 
-export const readTagTransferData = (dataTransfer: DataTransfer | null | undefined): string | null => {
+export const readTagTransferData = (dataTransfer?: DataTransfer | null): string | null => {
   if (!dataTransfer) {
     return null;
   }
diff --git a/frontend/src/documents/useEntryPointer.ts b/frontend/src/documents/useEntryPointer.ts
index 6cd7a1f..7a89665 100644
--- a/frontend/src/documents/useEntryPointer.ts
+++ b/frontend/src/documents/useEntryPointer.ts
@@ -26,8 +26,8 @@ export interface WorkspaceEntry {
 }
 
 interface UseEntryPointerOptions {
-  resolveDocumentRowKey?: (id: string | number) => string | null | undefined;
-  resolveFolderRowKey?: (id: string | number) => string | null | undefined;
+  resolveDocumentRowKey?: (id: string | number) => string | null;
+  resolveFolderRowKey?: (id: string | number) => string | null;
   onSelectEntry?: (entry: WorkspaceEntry, event?: PointerEventLike | null, metadata?: EntryPointerMetadata) => void;
   onInspectDocument?: (id: string | number, metadata?: EntryPointerMetadata) => void;
 }