Return null if cosmos db input can't find item

[florianlenz96]

Issue describing the changes in this PR

resolves #2545

Pull request checklist

• My changes do not require documentation changes
  • Otherwise: Documentation issue linked to PR
• My changes should not be added to the release notes for the next release
  • Otherwise: I've added my notes to release_notes.md
• My changes do not need to be backported to a previous version
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• I have added all required tests (Unit tests, E2E tests)

Additional information

Hi there,

it's my first PR in an open source repo. If I need to change anything or you have questions, please contact me.

Additional PR information

[florianlenz96]

@microsoft-github-policy-service agree

[jviau]

LGTM. Thank you for your contribution!

@liliankasem do you have any concerns with this being a breaking behavior change?

[liliankasem]

LGTM. Thank you for your contribution!

@liliankasem do you have any concerns with this being a breaking behavior change?

I think it could be for folks depending on the failure in this scenario, but then again it will be a failure in every scenario today so I don't think there would be any major/breaking impact?

[florianlenz96]

@liliankasem I've resolved your notes. Can you verify. Thanks in advance.

[liliankasem]

/azp run dotnet-worker.public

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[jviau]

/azp run extensions.cosmos.public

[azure-pipelines]

No pipelines are associated with this pull request.

[azure-pipelines]

No pipelines are associated with this pull request.

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[liliankasem]

@florianlenz96 thanks for contributing! Release is out: https://www.nuget.org/packages/Microsoft.Azure.Functions.Worker.Extensions.CosmosDB/4.12.0