Fix more empty return values

src/file/document/body/section-properties/properties/page-borders.ts

@@ -75,7 +75,7 @@ export class PageBorders extends IgnoreIfEmptyXmlComponent {
         super("w:pgBorders");
 
         if (!options) {
-            return;
+            return this;
         }
 
         if (options.pageBorders) {

src/file/paragraph/run/symbol-run.ts

@@ -11,7 +11,7 @@ export class SymbolRun extends Run {
         if (typeof options === "string") {
             super({});
             this.root.push(new Symbol(options));
-            return;
+            return this;
         }
 
         super(options);