fix: use undefined (#38046)

* fix: use undefined

* fix: use undefined

components/float-button/BackTop.tsx

@@ -76,7 +76,7 @@ const BackTop: React.FC<BackTopProps> = props => {
   const rootPrefixCls = getPrefixCls();
   const [wrapSSR] = useStyle(prefixCls);
 
-  const groupShape = useContext<FloatButtonShape | null>(FloatButtonGroupContext);
+  const groupShape = useContext<FloatButtonShape | undefined>(FloatButtonGroupContext);
 
   const mergeShape = groupShape || shape;
 

components/float-button/context.ts

@@ -1,7 +1,7 @@
 import React from 'react';
 import type { FloatButtonShape } from './interface';
 
-const FloatButtonGroupContext = React.createContext<FloatButtonShape | null>(null);
+const FloatButtonGroupContext = React.createContext<FloatButtonShape | undefined>(undefined);
 
 export const { Provider: FloatButtonGroupProvider } = FloatButtonGroupContext;
 

components/float-button/index.tsx

@@ -33,7 +33,7 @@ const FloatButton: React.ForwardRefRenderFunction<
     ...restProps
   } = props;
   const { getPrefixCls, direction } = useContext<ConfigConsumerProps>(ConfigContext);
-  const groupShape = useContext<FloatButtonShape | null>(FloatButtonGroupContext);
+  const groupShape = useContext<FloatButtonShape | undefined>(FloatButtonGroupContext);
   const prefixCls = getPrefixCls(floatButtonPrefixCls, customizePrefixCls);
   const [wrapSSR, hashId] = useStyle(prefixCls);