[master] Provide nil return support for the client generation when the response has no content type instead of giving http:Response

[lnash94]

Purpose

$ballerina-platform/ballerina-library#5720

Automation tests

• Unit tests - Added

  Code coverage information

• Integration tests

  Details about the test cases and coverage

Security checks

• Followed secure coding standards in http://wso2.com/technical-reports/wso2-secure-engineering-guidelines? yes/no
• Ran FindSecurityBugs plugin and verified report? yes/no
• Confirmed that this PR doesn't commit any keys, passwords, tokens, usernames, or other secrets? yes/no

Samples

Provide high-level details about the samples related to this feature

Related PRs

#1568

Migrations (if applicable)

Describe migration steps and platforms on which migration has been tested

Test environment

List all JDK versions, operating systems, databases, and browser/versions on which this feature/fix was tested

Learning

Describe the research phase and any blog posts, patterns, libraries, or add-ons you used to solve the problem.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6f46ee5) 80.10% compared to head (ed1ce59) 80.10%.

❗ Current head ed1ce59 differs from pull request most recent head 1f2b689. Consider uploading reports for the commit 1f2b689 to get more accurate results

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #1567   +/-   ##
=========================================
  Coverage     80.10%   80.10%           
- Complexity     1854     1862    +8     
=========================================
  Files           125      125           
  Lines         10323    10325    +2     
  Branches       1704     1708    +4     
=========================================
+ Hits           8269     8271    +2     
  Misses         1464     1464           
  Partials        590      590           

Files	Coverage Δ
.../io/ballerina/openapi/core/GeneratorConstants.java	92.03% <ø> (ø)
.../core/generators/client/FunctionBodyGenerator.java	94.53% <100.00%> (-0.07%)	⬇️
...generators/client/FunctionReturnTypeGenerator.java	69.04% <100.00%> (+1.14%)	⬆️

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[dilanSachi]

Approved as its the same PR sent fro 1.8.x