AlbTargetGroupRequest misses default value for headers

[miere]

Hi there!

I recently updated my ALB configuration, enabling the multi-header feature. This move introduced a breaking change, preventing me to handle ALB Requests. The root cause, if my diagnose is correct, lies in the fact that, with multi-header enabled in ALB, the header entry is empty and might've been removed during the serialization process. As a result, serde tries to deserialize the received bytes into an AlbTargetGroupRequest instance but fails as header is mandatory and has no default implementation available.

Here you can find the raw JSON that was received by the Lambda Runtime.

I know that the AlbTargetGroupRequest is generated based on the Go SDK, but for the sake of the test, I've manually patched it and it worked as expected.