Fix useCreate fails to update the cache when id equals 0

[ThieryMichel]

Problem

When creating a resource with a numeric id for the first time, it's id will be 0, and updateCache will interpret this as no id, breaking the creation

Solution

Test for id being undefined or null specifically

How To Test

In storybook go to the new story: http://localhost:9010/?path=/story/ra-core-dataprovider-usecreate--create-id-zero

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• The PR targets master for a bugfix or a documentation fix, or next for a feature
• The PR includes unit tests (if not possible, describe why)
• The PR includes one or several stories (if not possible, describe why)
• The documentation is up to date

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