Update-Metadata fails if specified value is an empty string

[AdmiringWorm]

Describe the bug

When calling Update-Metadata the call fails if the specified value is an empty string, even if that is intentional.

To Reproduce

1. Call Update-Metadata -key 'releaseNotes' -value '' with a nuspec file in the current directory and make sure the releaseNotes element exists.

Expected behavior

Did not expect the call to fail, but instead just set the elements inner text to empty (possibly with a warning).

Screenshots

Desktop (please complete the following information):

• OS: [e.g. Windows 10] Windows 10
• Version: [e.g. 0.3.0] 0.4.1
• Powershell version: PS 5.1.19041.1320
• AU Version: 2021.7.18

Additional context