refactor: use explicit comparisons

Author: ahmadalfy

lib/index.js

@@ -5,11 +5,11 @@ module.exports = function (options) {
     options = {}
   }
 
-  if (!options.classIgnore) {
+  if (options.classIgnore === undefined) {
     options.classIgnore = []
   }
 
-  if (!options.extensionIgnore) {
+  if (options.extensionIgnore === undefined) {
     options.extensionIgnore = []
   }