read_varchain returns undefined instead of null

coretool.js

@@ -236,8 +236,8 @@ module.exports = {
   },
 
   read_varchain (path, root) {
-    var parent = root || globalThis || global || window || {}
-    var names = path.split('.')
+    let parent = root || globalThis || global || window || {}
+    let names = path.split('.')
     for (var i in names) {
       if (typeof parent === 'object' && names[i].match(/^\w+\(\)$/) && typeof parent[names[i].substring(0, names[i].length - 2)] === 'function') {
         // 支持 xxx.myfunc().yyy 的函数形式作为一个路径节点。
@@ -245,10 +245,13 @@ module.exports = {
       } else if (typeof parent === 'object' && names[i].match(/^\w+$/) && typeof parent[names[i]] != 'undefined' && parent[names[i]] != null) {
         parent = parent[names[i]]
       } else {
-        return null
+        return undefined
       }
     }
-    return parent === null || parent === undefined ? null : parent
+    if (parent === null || parent === undefined || isNaN(parent) || typeof parent === 'number') {
+      return undefined
+    }
+    return parent
   },
 
   set_varchain (path, root, value) {