Unhandled exception when retrieving already built incompatible payload

[chamil321]

Description:
Execptions thrown from https://github.com/ballerina-platform/module-ballerina-http/blob/d5e06bea9b722923ac033491fffa711f70b28f7e/http-native/src/main/java/org/ballerinalang/net/http/nativeimpl/ExternHttpDataSourceBuilder.java#L92 are catched and processed with NULL balFuture

Steps to reproduce:

import ballerina/http;

service / on new http:Listener(8090) {
    resource function get stats/[string country]() returns json | error {
        http:Client diseaseEndpoint = check new ("http://api.worldbank.org/v2");
        string  path = string `/country/${country}/indicator/SP.POP.TOTL`;
        http:Response resp = check diseaseEndpoint -> get(path);
        return resp.getJsonPayload();
    }
}

error: java.lang.NullPointerException
        at ballerina.http.1_1_0-alpha8:externGetJson(http_commons.bal:340)
           ballerina.http.1_1_0-alpha8.Response:getJsonPayload(http_response.bal:205)
           chamil.covid19Package.0_1_0.$anonType$_0:$get$stats$*(main.bal:29)

Client

GET http://localhost:8090/stats/LK

Affected Versions:
beta1

OS, DB, other environment details and versions:

Related Issues (optional):

Suggested Labels (optional):

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[chamil321]

Observed this error with caching client. Caching client build the payload with as blob first. The program retrieves the payload as json. But the payload type is xml. The thrown error by the json parser is caught but processed with null balfuture.

Can be reproduced with

service / on inResponseCachedPayloadListener {
    resource function get checkJson() returns json|error {
        http:Client diseaseEndpoint = check new ("http://localhost:" + inResponseCachedPayloadTestBEPort.toString());
        http:Response resp = check diseaseEndpoint -> get("/getXml");
        byte[] b = check resp.getBinaryPayload(); // represents cache behaviour
        return resp.getJsonPayload();
    }
}

service / on inResponseCachedPayloadBEListener {
    resource function get getXml(http:Caller caller) {
        http:Response response = new;
        xml xmlStr = xml `<name>Ballerina</name>`;
        response.setXmlPayload(xmlStr);
        error? result = caller->respond(response);
    }
}

or

service / on inResponseCachedPayloadListener {
    resource function get checkJson() returns json|error {
        http:Client diseaseEndpoint = check new ("http://localhost:" + inResponseCachedPayloadTestBEPort.toString());
        http:Response resp = check diseaseEndpoint -> get("/getXml");
        return resp.getJsonPayload();
    }
}

service / on inResponseCachedPayloadBEListener {
    resource function get getXml(http:Caller caller) {
        http:Response response = new;
        xml xmlStr = xml `<name>Ballerina</name>`;
        response.setXmlPayload(xmlStr);
        // enables cache behaviour
        response.setHeader("Cache-Control", "public, max-age=14400");
        response.setHeader("etag", "W/\"25f-VB/B7cwRxpkTFPnufB0QcTCzHUE\"");
        error? result = caller->respond(response);
    }
}