fix(components): [select-v2] set model-value default to undefined (#21540)

* fix(components): [select-v2] set `model-value` default to `undefined`

* test: test

packages/components/select-v2/__tests__/select.test.ts

@@ -254,6 +254,15 @@ describe('Select', () => {
     )
   })
 
+  it('should show placeholder when no model-value setted', async () => {
+    const wrapper = _mount('<el-select :options="[]"></el-select>')
+    expect(
+      wrapper
+        .find('.el-select__selected-item.el-select__placeholder > span')
+        .text()
+    ).toBe('Select')
+  })
+
   it('default value', async () => {
     const wrapper = createSelect({
       data: () => ({

packages/components/select-v2/src/defaults.ts

@@ -136,6 +136,7 @@ export const selectV2Props = buildProps({
     type: definePropType<
       any[] | string | number | boolean | Record<string, any> | any
     >([Array, String, Number, Boolean, Object]),
+    default: undefined,
   },
   /**
    * @description is multiple