PR Summary

Regarding Invoke-WebRequest:

A change was made to PowerShell Core with commit 2285ece613 that changes the way web request headers are handled when the web request has no body. Previously, they would be ignored. Now, they are processed anyway, including the ContentType header, which makes no sense when there's no body. Now, the headers are processed anyway, and if there's a ContentType header with an empty string value, it will fail.

When a customer tries to pass in a blank (i.e., $null) ContentType to a function that takes a string because they have no body, it gets treated as an empty string, not $null.

This works fin in Windows PowerShell (PS5 and earlier) and PowerShell Core 6, because their code bases don't have commit 2285ece613.

When it fails, they get a message saying that they can avoid this by passing -SkipHeaderValidation, but this flag isn't available in Windows PowerShell, and using it would require a crude hard-coded version check to see if you're on Windows PowerShell or PowerShell Core.

This change merely skips adding headers to the request if the header value is nothing (null or whitespace).

Question: Should we only do this skip for the ContentType header?

Fix #11396

PR Context

Without this, PS scripts that run fine in Windows PowerShell and PowerShell Core 6 break.

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