Add nullable support

[RolandHewage]

Purpose

The AsyncAPI schema doesn't support nullable anymore. The idea is that OpenAPI and AsyncAPI will converge into standard JSON Schema in upcoming releases. Please refer [1], [2], [3]. But there are scenarios where the schema fields can be nullable which results in Ballerina data binding issues. Therefore it was decided to give nullable support in the AsyncAPI tool using the x-nullable: true extension in AsyncAPI schema. Refer email thread "[Discussion] Improve AsyncAPI tool to support nullable fields in AsyncAPI schema".

[1] asyncapi/spec#204 (comment)
[2] asyncapi/generator#33
[3] https://www.asyncapi.com/docs/reference/specification/v2.0.0#schemaObject

 x-nullable: true

Resolves https://github.com/wso2-enterprise/choreo/issues/13846

Goals

Add nullable support

Approach

Add nullable support in schema generation

User stories

Support scenarios where nullable fields are present in AsyncAPI schema

Release note

Add nullable support

Automation tests

• Unit tests

  Done

• Integration tests

  Done

Security checks

• Followed secure coding standards in http://wso2.com/technical-reports/wso2-secure-engineering-guidelines? yes
• Ran FindSecurityBugs plugin and verified report? yes
• Confirmed that this PR doesn't commit any keys, passwords, tokens, usernames, or other secrets? yes

Test environment

Ballerina Version: 2201.1.0
Operating System: Ubuntu 20.04
Java SDK: 11

[codecov]

Codecov Report

Base: 0.00% // Head: 0.00% // No change to project coverage 👍

Coverage data is based on head (50b49d6) compared to base (decad01).
Patch coverage: 0.00% of modified lines in pull request are covered.

Additional details and impacted files

@@          Coverage Diff          @@
##            main     #55   +/-   ##
=====================================
  Coverage   0.00%   0.00%           
=====================================
  Files         27      28    +1     
  Lines        851     947   +96     
  Branches      72      85   +13     
=====================================
- Misses       851     947   +96     

Impacted Files	Coverage Δ
...ncapi/codegenerator/application/CodeGenerator.java	0.00% <0.00%> (ø)
...syncapi/codegenerator/configuration/Constants.java	0.00% <ø> (ø)
...degenerator/controller/AsyncApiSpecController.java	0.00% <0.00%> (ø)
...codegenerator/controller/DispatcherController.java	0.00% <0.00%> (ø)
...nerator/usecase/ExtractIdentifierPathFromSpec.java	0.00% <0.00%> (ø)
...nerator/usecase/ExtractIdentifierTypeFromSpec.java	0.00% <0.00%> (ø)
...r/usecase/GenerateModuleMemberDeclarationNode.java	0.00% <0.00%> (ø)

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[github-actions]

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[github-actions]

This PR has been open for more than 15 days with no activity. This will be closed in 3 days unless the stale label is removed or commented.

[github-actions]

This PR has been open for more than 15 days with no activity. This will be closed in 3 days unless the stale label is removed or commented.