update readme

packages/components/src/popover/README.md

@@ -61,7 +61,7 @@ Set this prop to `false` to disable focus changing entirely. This should only be
 
 ### placement
 
-The direction in which the popover should open relative to its parent node or anchor node. 
+The direction in which the popover should open relative to its parent node or anchor node.
 
 The available base placements are 'top', 'right', 'bottom', 'left'.
 
@@ -137,7 +137,7 @@ A callback function which is used to override the anchor value computation algor
 
 If you need the `DOMRect` object i.e., the position of popover to be calculated on every time, the popover re-renders, then use `getAnchorRect`.
 
-`getAnchorRect` callback function receives a reference to the popover anchor element as a function parameter and it should return a `DOMRect` object.
+`getAnchorRect` callback function receives a reference to the popover anchor element as a function parameter and it should return a `DOMRect` object. Noting that `getAnchorRect` can be called with `null`.
 
 -   Type: `Function`
 -   Required: No