DefaultCommandPrefix from Module PSD ignored after recent patch #25419

Prerequisites

• Write a descriptive title.
• Make sure you are able to repro it on the latest released version
• Search the existing issues.
• Refer to the FAQ.
• Refer to Differences between Windows PowerShell 5.1 and PowerShell.

Steps to reproduce

• Import a PowerShell module with a DefaultCommandPrefix set in the .psd file
• As an example, use my module totkeks.GitManagement from PowerShell gallery
• Run command Set-GitBaseDirectory

Source of the error from this PR #20409 (comment), where it is not checking for String.IsNullOrEmpty() anymore, instead using just null coalescing ??, which doesn't include String.Empty.

Expected behavior

* Commands are prefixed with the defined prefix, e.g. `Git`, and are working / found in the current scope

Actual behavior

* Command not found, because the prefix was overwritten with an empty string

Error details

Environment data

$PSVersionTable

Name                           Value
----                           -----
PSVersion                      7.6.0-preview.4
PSEdition                      Core
GitCommitId                    7.6.0-preview.4
OS                             Microsoft Windows 10.0.26200
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

Visuals

No response