fix: headers with null values removed from response

[ekruczek]

Issue #1522

• remove response header if set with null value.
• ignore null values when added to response header

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[vicheey]

LGTM. Waiting workflow result.

[erikpragt-connectid]

Thanks for merging this. Are there any snapshots we can use, or should we wait for a new release?

[reedham-aws]

Thanks for merging this. Are there any snapshots we can use, or should we wait for a new release?

This fix has been released in version 2.1.5