fix: make getter safe when patching a property

lib/common/utils.ts

@@ -106,6 +106,9 @@ export function patchProperty(obj: any, prop: string) {
   // The getter would return undefined for unassigned properties but the default value of an
   // unassigned property is null
   desc.get = function() {
+    if (this == null) {
+      return this;
+    }
     let r = this[_prop] || null;
     // result will be null when use inline event attribute,
     // such as <button onclick="func();">OK</button>