Fix tests and use proper types for disregarding XMLComponent

src/export/formatter.ts

@@ -2,6 +2,12 @@ import { BaseXmlComponent, IXmlableObject } from "file/xml-components";
 
 export class Formatter {
     public format(input: BaseXmlComponent): IXmlableObject {
-        return input.prepForXml();
+        const output = input.prepForXml();
+
+        if (output) {
+            return output;
+        } else {
+            throw Error("XMLComponent did not format correctly");
+        }
     }
 }