Fix merge behaviour when the value is null

Utils.ts

@@ -210,7 +210,9 @@ export class Utils {
             if (sourceV?.length !== undefined && targetV?.length !== undefined && key.startsWith("+")) {
                 target[key] = targetV.concat(sourceV)
             } else if (typeof sourceV === "object") {
-                if (targetV === undefined) {
+                if (sourceV === null) {
+                    target[key] = null
+                } else if (targetV === undefined) {
                     target[key] = sourceV;
                 } else {
                     Utils.Merge(sourceV, targetV);
@@ -364,7 +366,9 @@ export class Utils {
         let file;
         if (typeof (contents) === "string") {
             file = new Blob([contents], {type: 'text/plain'});
-        }else {file = contents;}
+        } else {
+            file = contents;
+        }
         element.href = URL.createObjectURL(file);
         element.download = fileName;
         document.body.appendChild(element); // Required for this to work in FireFox

test/Utils.spec.ts

@@ -2,6 +2,8 @@ import T from "./TestHelper";
 import {Utils} from "../Utils";
 import {equal} from "assert";
 import LZString from "lz-string";
+import * as Assert from "assert";
+import * as assert from "assert";
 
 export default class UtilsSpec extends T {
     private static readonly example = {
@@ -104,6 +106,16 @@ export default class UtilsSpec extends T {
                 equal(result.list1[1], "appended")
                 equal(result.list2.length, 1)
                 equal(result.list2[0], "should-be-untouched")
+            }],
+            ["Test merge with null", () => {
+                const obj = {
+                    someValue: 42
+                }
+                const override = {
+                    someValue: null
+                }
+                Utils.Merge(override, obj)
+                equal(obj.someValue, null)
             }]
         ]);
     }