IDE0072: False positive when using switch expression over a Nullable<T>, where both null and T cases are present

[airbreather]

Version Used:
.NET SDK 5.0.102

Steps to Reproduce:
dotnet build the following:

Program.cs

double? DivideByTwo(ulong? x)
{
    return x switch
    {
        null => null,
        ulong val => val / 2.0,
    };
}

ConsoleApp0.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net5.0</TargetFramework>
    <EnforceCodeStyleInBuild>true</EnforceCodeStyleInBuild>
  </PropertyGroup>

</Project>

.editorconfig

[*.cs]
dotnet_diagnostic.IDE0072.severity = warning

Expected Behavior:
IDE0072 is not raised: all cases are handled

Actual Behavior:
IDE0072 is raised. The suggested fix is to add a default case (discard) at the end.

Based on #50982 (comment), I suspect that this may have the same root cause as both that issue and #48876, but I'm logging it separately for now just in case it does happen to be different enough.