Update convertHeaders to use filter

Co-authored-by: AllanZhengYP <[email protected]>

Author: JordonPhillips

smithy-typescript-ssdk-libs/server-apigateway/src/lambda.ts

@@ -42,18 +42,8 @@ export function convertResponse(response: HttpResponse) : APIGatewayProxyResultV
     }
 }
 
-function convertHeaders(headers: APIGatewayProxyEventHeaders): HeaderBag {
-    const retVal: {[key: string]: string} = {};
-
-    for (const key in headers) {
-        const val = headers[key];
-        if (val !== undefined) {
-            retVal[key] = val;
-        }
-    }
-
-    return retVal;
-}
+const convertHeaders = (headers: APIGatewayProxyEventHeaders): HeaderBag => 
+        Object.fromEntries(Object.entries(headers).filter(([key, value]) => value !== undefined));
 
 function convertQuery(params: APIGatewayProxyEventQueryStringParameters | undefined): QueryParameterBag | undefined {
     if (params === undefined) {