Minor lint fixes

src/js/proxified-containers.js

@@ -1,10 +1,10 @@
 //Below lets us print errors, huge thanks to Jonothan @ https://stackoverflow.com/questions/18391212/is-it-not-possible-to-stringify-an-error-using-json-stringify
-if (!('toJSON' in Error.prototype))
+if (!("toJSON" in Error.prototype))
-Object.defineProperty(Error.prototype, 'toJSON', {
+  Object.defineProperty(Error.prototype, "toJSON", {
-    value: function () {
+    value: function() {
-        var alt = {};
+      let alt = {};
 
-        Object.getOwnPropertyNames(this).forEach(function (key) {
+      Object.getOwnPropertyNames(this).forEach(function(key) {
         alt[key] = this[key];
       }, this);
 
@@ -12,7 +12,7 @@ Object.defineProperty(Error.prototype, 'toJSON', {
     },
     configurable: true,
     writable: true
-});
+  });
 
 
 //This object allows other scripts to access the list mapping containers to their proxies
@@ -61,7 +61,7 @@ window.proxifiedContainers = {
         } else {
           const val = results_array.find(o => o.cookieStoreId === cookieStoreId);
 
-          if (typeof val !== "object" ) {
+          if (typeof val !== "object" || val === null) {
             reject({
               error: "doesnotexist",
               message: ""