COM PackageVersionInfo null deference bug

[luke-patchblox]

Brief description of your issue

When attempting to use PackageVersionInfo.GetMetadata, if there is a key that has a empty/null value the program using COM will terminate with a deference error. This is due to the lack of a null check inside of PackageVersionInfo::GetMetadata() inside of PackageVersionInfo.cpp in the Microsoft.Management.Deployment project.

Note: I fixed it by adding a check to see if the find could not find any value

My solution:

 hstring PackageVersionInfo::GetMetadata(winrt::Microsoft::Management::Deployment::PackageVersionMetadataField const& metadataField)
 {
     ::AppInstaller::Repository::PackageVersionMetadata metadataKey = GetRepositoryPackageVersionMetadata(metadataField);
     ::AppInstaller::Repository::IPackageVersion::Metadata metadata = m_packageVersion->GetMetadata();
     auto result = metadata.find(metadataKey);
     //Added: Had to add a check here to see if the result was empty
     if (result == metadata.end())
     {
         return winrt::to_hstring("");
     }

     hstring resultString = winrt::to_hstring(result->second);
     // The api uses "System" rather than "Machine" for install scope.
     if (metadataField == PackageVersionMetadataField::InstalledScope && resultString == L"Machine")
     {
         return winrt::to_hstring(L"System");
     }
     return resultString;
 }

Steps to reproduce

Use COM and call something like:
string silentUninstallString = match.CatalogPackage.InstalledVersion.GetMetadata(PackageVersionMetadataField.SilentUninstallCommand);

(Note: match is the MatchResult for searching for dbeaver.dbeaver)

Do a local package search and call this on something you have installed. I would recommend using dbeaver.dbeaver as it does not have a silent uninstall command in the registry and will cause the error.

Expected behavior

Should gracefully handle a particular key not having a value.

Actual behavior

Causes program to terminate ungracefully.

Environment

Windows Package Manager v1.10.340
Copyright (c) Microsoft Corporation. All rights reserved.

Windows: Windows.Desktop v10.0.26100.3476
System Architecture: X64
Package: Microsoft.DesktopAppInstaller v1.25.340.0

Winget Directories
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Logs                               %LOCALAPPDATA%\Packages\Microsoft.DesktopAppInstaller_8wekyb3d8bbwe\LocalState\Diag…
User Settings                      %LOCALAPPDATA%\Packages\Microsoft.DesktopAppInstaller_8wekyb3d8bbwe\LocalState\sett…
Portable Links Directory (User)    %LOCALAPPDATA%\Microsoft\WinGet\Links
Portable Links Directory (Machine) C:\Program Files\WinGet\Links
Portable Package Root (User)       %LOCALAPPDATA%\Microsoft\WinGet\Packages
Portable Package Root              C:\Program Files\WinGet\Packages
Portable Package Root (x86)        C:\Program Files (x86)\WinGet\Packages
Installer Downloads                %USERPROFILE%\Downloads
Configuration Modules              %LOCALAPPDATA%\Microsoft\WinGet\Configuration\Modules

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