spring-boot - Understanding difference between Custom Handler and SpringBootApiGatewayRequestHandler

Question

I'm new to Spring Cloud Function and came across it as one of best solution for developing FaaS based solution. I am specifically writing application for AWS Lambda Service which is back-end of API Gateway. I ran into very interesting problem with My test application and it is around Handler. My test application works well with Custom Handler written as -

public class UserProfileHandler extends SpringBootRequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {
}

which works well when configured as Handler in the AWS Lambda. Then I came across org.springframework.cloud.function.adapter.aws.SpringBootApiGatewayRequestHandler which is available in Spring Cloud Function dependency, so I wanted to get rid of UserProfileHandler hence I changed Handler configuration in AWS Lambda to org.springframework.cloud.function.adapter.aws.SpringBootApiGatewayRequestHandler instead of ...UserProfileHandler and now lambda fails with following error message. Has anyone run into this problem?

{
  "errorMessage": "java.util.Optional cannot be cast to com.amazonaws.services.lambda.runtime.events.APIGatewayProxyRequestEvent",
  "errorType": "java.lang.ClassCastException",
  "stackTrace": [
    "com.transformco.hs.css.userprofile.function.UserProfileFunction.apply(UserProfileFunction.java:16)",
    "org.springframework.cloud.function.context.catalog.BeanFactoryAwareFunctionRegistry$FunctionInvocationWrapper.invokeFunction(BeanFactoryAwareFunctionRegistry.java:499)",
    "org.springframework.cloud.function.context.catalog.BeanFactoryAwareFunctionRegistry$FunctionInvocationWrapper.lambda$doApply$1(BeanFactoryAwareFunctionRegistry.java:543)",
    "reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onNext(FluxMapFuseable.java:107)",
    "reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onNext(FluxMapFuseable.java:121)",
    "reactor.core.publisher.FluxJust$WeakScalarSubscription.request(FluxJust.java:99)",
    "reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.request(FluxMapFuseable.java:162)",
    "reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.request(FluxMapFuseable.java:162)",
    "reactor.core.publisher.BlockingIterable$SubscriberIterator.onSubscribe(BlockingIterable.java:218)",
    "reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onSubscribe(FluxMapFuseable.java:90)",
    "reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onSubscribe(FluxMapFuseable.java:90)",
    "reactor.core.publisher.FluxJust.subscribe(FluxJust.java:70)",
    "reactor.core.publisher.InternalFluxOperator.subscribe(InternalFluxOperator.java:53)",
    "reactor.core.publisher.BlockingIterable.iterator(BlockingIterable.java:80)",
    "org.springframework.cloud.function.adapter.aws.SpringBootRequestHandler.result(SpringBootRequestHandler.java:59)",
    "org.springframework.cloud.function.adapter.aws.SpringBootRequestHandler.handleRequest(SpringBootRequestHandler.java:52)",
    "org.springframework.cloud.function.adapter.aws.SpringBootApiGatewayRequestHandler.handleRequest(SpringBootApiGatewayRequestHandler.java:140)",
    "org.springframework.cloud.function.adapter.aws.SpringBootApiGatewayRequestHandler.handleRequest(SpringBootApiGatewayRequestHandler.java:43)"
  ]
}