fix: ensure totype always returns stringified null/undefined when null/undefined is passed (#30383)

js/tests/unit/util/index.spec.js

@@ -198,8 +198,9 @@ describe('Util', () => {
   })
 
   describe('typeCheckConfig', () => {
+    const namePlugin = 'collapse'
+
     it('should check type of the config object', () => {
-      const namePlugin = 'collapse'
       const defaultType = {
         toggle: 'boolean',
         parent: '(string|element)'
@@ -213,6 +214,34 @@ describe('Util', () => {
         Util.typeCheckConfig(namePlugin, config, defaultType)
       }).toThrow(new Error('COLLAPSE: Option "parent" provided type "number" but expected type "(string|element)".'))
     })
+
+    it('should return null stringified when null is passed', () => {
+      const defaultType = {
+        toggle: 'boolean',
+        parent: '(null|element)'
+      }
+      const config = {
+        toggle: true,
+        parent: null
+      }
+
+      Util.typeCheckConfig(namePlugin, config, defaultType)
+      expect().nothing()
+    })
+
+    it('should return undefined stringified when undefined is passed', () => {
+      const defaultType = {
+        toggle: 'boolean',
+        parent: '(undefined|element)'
+      }
+      const config = {
+        toggle: true,
+        parent: undefined
+      }
+
+      Util.typeCheckConfig(namePlugin, config, defaultType)
+      expect().nothing()
+    })
   })
 
   describe('makeArray', () => {