https://github.com/dotnet/sdk/blob/92850cff8424c2c7fb65ededa840acf2e5cac3c8/src/Tasks/Microsoft.NET.Build.Tasks/GenerateGlobalUsings.cs#L16C25-L16C31
The task shouldn't return nulls in the string array.
No customer impact as msbuild then later automatically trims the null elements when being passed around.