Fix the issue with empty array replacement

[chuangw6]

Changes

Prior to this change, if there is only one element in an array that is
a reference to an empty array, the original array becomes nil after
replacement, but it should be an empty array instead of nil.

Fixes #5149

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Release Notes

After the replacement with an empty array, the original array will be empty.

Example:
---
params:
  - name: myarray
     value: "$(params.anEmptyArray[*])"

[chuangw6]

/kind bug

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[abayer]

/lgtm

I'm always sad when we can't do var slice []..., but this is a legitimate reason to do so. =)

[abayer]

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[ywluogg]

/lgtm