Update README.md

tannerlinsley · web-flow · commit 8d4deb34969c · 2017-09-01T16:05:33.000-06:00
Fixes TanStack#475
diff --git a/README.md b/README.md
@@ -577,6 +577,8 @@ Every single built-in component's props can be dynamically extended using any on
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 ```
 
+If used, **a callback prop must return an valid object**, even if it's an empty one.
+
 These callbacks are executed with each render of the element with four parameters:
  1. Table State
  2. RowInfo (undefined if not applicable)
