Turn back on no-null-keyword. Use empty object instead of null to signal to the xml library that an empty element should be produced. Update the related tests.

Related to #306

src/file/xml-components/imported-xml-component.spec.ts

@@ -73,7 +73,7 @@ describe("ImportedXmlComponent", () => {
                         },
                     },
                     {
-                        "w:child": null,
+                        "w:child": {},
                     },
                 ],
             });