Making CosmosPatchOperations thread-safe

[FabianMeiswinkel]

Description

CosmosPatchOperations is not thread-safe - this can result in NullPointerExceptions (see below) when customers do patch operations (point operation on single document) and add path instructions concurrently from multiple threads.

java.lang.NullPointerException: null
        at com.azure.cosmos.implementation.patch.PatchUtil.cosmosPatchToJsonSerializable(PatchUtil.java:43)
        at com.azure.cosmos.implementation.patch.PatchUtil.serializeCosmosPatchToByteArray(PatchUtil.java:22)
        at com.azure.cosmos.implementation.RxDocumentClientImpl.patchDocumentInternal(RxDocumentClientImpl.java:1914)
        at com.azure.cosmos.implementation.RxDocumentClientImpl.lambda$patchDocument$46(RxDocumentClientImpl.java:1896)
        at com.azure.cosmos.implementation.ObservableHelper.lambda$inlineIfPossibleAsObs$1(ObservableHelper.java:44)
        at com.azure.cosmos.implementation.BackoffRetryUtility.lambda$executeRetry$0(BackoffRetryUtility.java:36)

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

[azure-sdk]

API change check

API changes are not detected in this pull request.

[xinlian12]

LGTM, thanks for the quick fix 👍