better handle in case of null and undefined result

Author: xinghengwang

lib/index.js

@@ -251,15 +251,15 @@ function translateLambdaResultIfNeeded(result, isV1) {
     return result;
   }
 
-  if (!result.statusCode && (typeof result === 'object' || typeof result === 'string')) {
+  if ((!result || !result.statusCode) && (typeof result === 'object' || typeof result === 'string' || typeof result === 'undefined')) {
     return {
-      "isBase64Encoded": false,
-      "statusCode": 200,
-      "body": JSON.stringify(result),
-      "headers": {
-        "content-type": "application/json"
+      isBase64Encoded: false,
+      statusCode: 200,
+      body: typeof result === 'undefined' ? undefined : JSON.stringify(result),
+      headers: {
+        'content-type': 'application/json'
       }
-    }
+    };
   }
 
   return result || {};