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src/FillSpace.jsx

@@ -260,13 +260,14 @@ class FillSpace extends Component {
 
     // FillSpace owns current page, wheel-pagination and the pagination header.
     // Caller feeds `items` plus one row element via `renderItem` (component
-    // type or callback).
+    // type or callback). `items` may be undefined while data is loading.
     const { pageSize, currentPage, viewportHeight } = this.state;
-    const total = items.length;
+    const list = Array.isArray(items) ? items : [];
+    const total = list.length;
     const pageCount = Math.max(1, Math.ceil(total / Math.max(1, pageSize)));
     const safePage = Math.min(Math.max(1, currentPage), pageCount);
     const offset = (safePage - 1) * pageSize;
-    const pageItems = items.slice(offset, offset + pageSize);
+    const pageItems = list.slice(offset, offset + pageSize);
     const showPagination = total > pageSize;
     // Hidden data-free probe: measures `renderItem` itself (no data).
     const probe = renderProbeElement(renderItem);