Fix startSession

packages/libs/extension-base/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@autorest/extension-base",
-  "version": "3.4.3",
+  "version": "3.4.4",
   "description": "Library for creating AutoRest extensions",
   "main": "dist/index.js",
   "exports": {

packages/libs/extension-base/src/session.ts

@@ -155,8 +155,9 @@ export async function startSession<TInputModel>(
   artifactType?: string,
 ) {
   // This is just to make it work with older version so the older method definition is also valid.
-  if (schema === undefined || (schema as any) === {}) {
+  if (artifactType?.constructor.name === "Schema") {
     schema = artifactType as any;
+    artifactType = undefined;
   }
   const { model, filename } = await getModel<TInputModel>(host, schema, artifactType);
   const configuration = await host.getValue("");