AWS Lambda Test S3 Event Notification is Null - amazon-web-services

Question

I have the following Kotlin code:
override fun execute(input: APIGatewayProxyRequestEvent): APIGatewayProxyResponseEvent {
val response = APIGatewayProxyResponseEvent()
val body = input.body
if(body != null) {
val json = JSONObject(body)
val s3 = json.optJSONArray("Records").getJSONObject(0).getJSONObject("s3")
val bucketName = s3.getJSONObject("bucket").getString("name")
try {
val jsonResponse = objectMapper.writeValueAsString(mapOf("message" to bucketName))
response.statusCode = 200
response.body = jsonResponse
} catch (e: JsonProcessingException) {
response.statusCode = 500
}
}
return response
}
I want to basically get the function to be triggered on a new S3 put and just get the bucket name. When I try locally to pass a APIGatewayProxyRequestEvent with the following body:
{
"Records": [
{
"eventVersion": "2.0",
"eventSource": "aws:s3",
"awsRegion": "us-east-1",
"eventTime": "1970-01-01T00:00:00.000Z",
"eventName": "ObjectCreated:Put",
"userIdentity": {
"principalId": "EXAMPLE"
},
"requestParameters": {
"sourceIPAddress": "127.0.0.1"
},
"responseElements": {
"x-amz-request-id": "EXAMPLE123456789",
"x-amz-id-2": "EXAMPLE123/5678abcdefghijklambdaisawesome/mnopqrstuvwxyzABCDEFGH"
},
"s3": {
"s3SchemaVersion": "1.0",
"configurationId": "testConfigRule",
"bucket": {
"name": "example-bucket",
"ownerIdentity": {
"principalId": "EXAMPLE"
},
"arn": "arn:aws:s3:::example-bucket"
},
"object": {
"key": "test%2Fkey",
"size": 1024,
"eTag": "0123456789abcdef0123456789abcdef",
"sequencer": "0A1B2C3D4E5F678901"
}
}
}
]
}
The kotlin code works as expected. When I deploy this on AWS lambda, and I either provide the exact same body in a test event or actually uploading an object on S3 to trigger the function, the input.body is null. I don't understand why.