fix: fix unwanted crash when not supplying an error path

src/cli.ts

@@ -82,7 +82,7 @@ commander
       // tslint:disable-next-line:no-magic-numbers
       writeFileSync(errPath, JSON.stringify(result.errors, null, 2));
       Logger.ok(`Mapping errors written to ${errPath}.`);
-    } else {
+    } else if (result.errors.length > 0) {
       for (const error of result.errors) {
         await Logger.error(error);
       }