fix(option): skip nil bytes for CredentialsJSON

[lexcao]

Closes #2647
Nil bytes was treated to empty bytes, which causes failure on empty JSON.
I think we can improve this by ignoring nil bytes.

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[quartzmo]

@lexcao Please create a bug report (or possibly, feature request, depending on how you view this), we need that before we can move forward with this PR.

[quartzmo]

In your issue, please explain why you think adding the conditional to avoid setting the nil value needs to be in this package, and not just in the user code such as in your PR authzed/spicedb#1948.

[lexcao]

Hi @quartzmo
Thanks for reviewing, let me create an issue to provide more context first!

[lexcao]

Hi @quartzmo
I have created an issue #2647.
Please help review.
Thanks!

[codyoss]

I am going to close this as I opened up an alternative PR, thank you for the report though!