fix el null

Author: iPeng6

package.json

@@ -1,6 +1,6 @@
 {
   "name": "docsify-sidebar-collapse",
-  "version": "1.0.4",
+  "version": "1.0.6",
   "description": "sidebar-collapse plugin for docsify",
   "main": "src",
   "scripts": {

src/index.js

@@ -4,14 +4,16 @@ $docsify.plugins = [
   function(hook, vm) {
     hook.doneEach(function(html, next) {
       let el = document.querySelector('.sidebar-nav .active');
-      el.classList.add('open');
-      while (el && el.className !== 'sidebar-nav') {
-        if (el.parentElement.tagName === 'LI') {
-          el.parentElement.className = 'open';
+      if (el) {
+        el.classList.add('open');
+        while (el.className !== 'sidebar-nav') {
+          if (el.parentElement.tagName === 'LI') {
+            el.parentElement.className = 'open';
+          }
+          el = el.parentElement;
         }
-        el = el.parentElement;
       }
       next(html);
     });
-  },
+  }
 ].concat($docsify.plugins || []);