Message : Attempted to send invalid data through http response. Error type : MULE:SOURCE_RESPONSE_SEND

<?xml version="1.0" encoding="UTF-8"?>

<mule xmlns:db="http://www.mulesoft.org/schema/mule/db" xmlns:http="http://www.mulesoft.org/schema/mule/http"

xmlns="http://www.mulesoft.org/schema/mule/core"

xmlns:doc="http://www.mulesoft.org/schema/mule/documentation" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.mulesoft.org/schema/mule/core http://www.mulesoft.org/schema/mule/core/current/mule.xsd

http://www.mulesoft.org/schema/mule/http http://www.mulesoft.org/schema/mule/http/current/mule-http.xsd

http://www.mulesoft.org/schema/mule/db http://www.mulesoft.org/schema/mule/db/current/mule-db.xsd">

<http:listener-config name="HTTP_Listener_config" doc:name="HTTP Listener config" doc:id="3e081917-1381-4106-a2fa-a9c4d8180881" >

<http:listener-connection host="0.0.0.0" port="8081" />

</http:listener-config>

<db:config name="Database_Config" doc:name="Database Config" doc:id="4be42af6-7e1c-4b97-b5ed-6718d5aaf398" >

<db:my-sql-connection host="mudb.learn.mulesoft.com" port="3306" user="mule" password="mule" database="training"/>

</db:config>

<flow name="training4-american-wsFlow" doc:id="0fe44c96-8928-4eed-83ae-937a742fc24e" >

<http:listener doc:name="Listener" doc:id="43e1d8fb-4de1-4173-8ec9-5666c480529b" config-ref="HTTP_Listener_config" path="/flights"/>

<db:select doc:name="Select" doc:id="74c0406a-9130-445f-95f5-5a4ff5b01fee" config-ref="Database_Config">

<db:sql >SELECT *

FROM american</db:sql>

</db:select>

</flow>

</mule>