Handle tables that don't have decorations.

packages/flutter/lib/src/rendering/table.dart

@@ -891,6 +891,7 @@ class RenderTable extends RenderBox {
       for (int y = 0; y < rows; y += 1) {
         if (_rowDecorations.length <= y)
           break;
+        if (_rowDecorations[y] != null) {
           _rowDecorationPainters[y] ??= _rowDecorations[y].createBoxPainter();
           _rowDecorationPainters[y].paint(canvas, new Rect.fromLTRB(
             offset.dx,
@@ -900,6 +901,7 @@ class RenderTable extends RenderBox {
           ));
         }
       }
+    }
     for (int index = 0; index < _children.length; index += 1) {
       RenderBox child = _children[index];
       if (child != null) {

packages/flutter/lib/src/widgets/table.dart

@@ -47,7 +47,9 @@ class Table extends RenderObjectWidget {
     this.defaultVerticalAlignment: TableCellVerticalAlignment.top,
     this.textBaseline
   }) : children = children,
-       _rowDecorations = children.map/*<Decoration>*/((TableRow row) => row.decoration).toList(),
+       _rowDecorations = children.any((TableRow row) => row.decoration != null)
+                         ? children.map/*<Decoration>*/((TableRow row) => row.decoration).toList()
+                         : null,
        super(key: key) {
     assert(children != null);
     assert(defaultColumnWidth != null);