fix optional fields in json

[phshah95]

Issue #, if available:

Description of changes:

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[phshah95]

@mohitpali any chance you can leave some feedback on this small change? It is preventing us from using schemas like the one defined in the test. Thank you

[phshah95]

also not sure why that schema is being parsed as anyOf instead of oneOf..maybe the fix is there instead. Although, it does seem logical to included anyOf in this check too.

[YangSan0622]

Hello, do you mind create a issue to describe the problem we are trying to resolve here so we can have more context before we start the review process?

[phshah95]

made an issue here @YangSan0622

[mohitpali]

Please add unit tests or fix them to help us understand the issue better - tests are failing with error -

 [INFO] Running com.amazonaws.services.schemaregistry.kafkaconnect.jsonschema.ToConnectTest
Error:  Tests run: 62, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 0.098 s <<< FAILURE! - in com.amazonaws.services.schemaregistry.kafkaconnect.jsonschema.ToConnectTest
Error:  testSchemaCache_size_toConnectConversion  Time elapsed: 0.011 s  <<< FAILURE!
org.opentest4j.AssertionFailedError: expected: <1> but was: <0>

[YangSan0622]

It looks like the test failure mentioned is still there. Do we know what is going on?