Issue 5039 - add support of nullable non-object values in settings

lib/prefs.js

Index: lib/prefs.js
diff --git a/lib/prefs.js b/lib/prefs.js
index 00c52ea82147125ea94eb4005b6c3f7b5a78d123..a4618868753f05927aec825ed2089e4aaaba1bed 100644
--- a/lib/prefs.js
+++ b/lib/prefs.js
@@ -46,7 +46,14 @@ let defaults = {
   disable_auto_updates: false,
   first_run_subscription_auto_select: true,
   notifications_ignoredcategories: [],
-  allowed_connection_type: ""
+  allowed_connection_type: null
+};
+
+// It is for non-objects, e.g. for string, number, etc.
+// Don't put here preferences used by adblockpluscore.
+let nullableValues_ExpectedTypes = {
+  __proto__: null,
+  allowed_connection_type: "string"
 };
 
 let preconfigurable = ["suppress_first_run_page", "disable_auto_updates",
@@ -58,6 +65,14 @@ let listeners = [];
 let isDirty = false;
 let isSaving = false;
 
+function isValueTypeCorrect(key, value)
+{
+  let nullableValue_ExpectedType = nullableValues_ExpectedTypes[key];
+  return !nullableValue_ExpectedType ?
+    typeof value == typeof defaults[key] :
+    value === null || typeof value == nullableValue_ExpectedType;
+}
+
 function defineProperty(key)
 {
   Object.defineProperty(Prefs, key,
@@ -65,7 +80,7 @@ function defineProperty(key)
     get: () => values[key],
     set: function(value)
     {
-      if (typeof value != typeof defaults[key])
+      if (!isValueTypeCorrect(key, value))
         throw new Error("Attempt to change preference type");
 
       if (value == defaults[key])
@@ -142,7 +157,13 @@ let Prefs = exports.Prefs = {
 // Update the default prefs with what was preconfigured
 for (let key in _preconfiguredPrefs)
   if (preconfigurable.indexOf(key) != -1)
-    defaults[key] = _preconfiguredPrefs[key];
+  {
+    let value = _preconfiguredPrefs[key];
+    if (!isValueTypeCorrect(key, value))
+      throw new Error("Unexpected value type in preconfigured preferences");
+
+    defaults[key] = value;
+  }
 
 // Define defaults
 for (let key in defaults)