public Optional<String> getRequestParameter(String expression) {
        return Optional.ofNullable(requestParameters.get(expression));
    }
Get a specific request parameter by input expression.

@param expression Expression to get.
@return Returns the optionally found request parameter.
smithy-aws-apigateway-traits/src/main/java/software/amazon/smithy/aws/apigateway/traits/IntegrationTrait.java