gistfile1.bas

Public Class Class1
    Private Delegate Sub AnEventHandler(Of T)(ByVal newValue As T)

    Private Event A As AnEventHandler(Of Integer) 'Works
    Private Event B As AnEventHandler(Of Guid) 'Works
    Private Event C As AnEventHandler(Of Foo) 'Works
    
    Private Event D As AnEventHandler(Of Bar(Of Integer)) 'Works
    Private Event E As AnEventHandler(Of Bar(Of Guid)) 'Works
    Private Event F As AnEventHandler(Of Bar(Of Foo)) 'Works
    
    Private Event G As AnEventHandler(Of Baz(Of Integer)) 'Works
    Private Event H As AnEventHandler(Of Baz(Of Guid)) 'Works
    Private Event I As AnEventHandler(Of Baz(Of Foo)) 'Works
    
    Private Event J As AnEventHandler(Of Nullable(Of Integer)) 'Works
    'Private Event K As AnEventHandler(Of Nullable(Of Guid)) 'Fails
    'Private Event K As AnEventHandler(Of Nullable(Of Foo)) 'Fails
End Class

Public Structure Foo
    Public x As Integer
End Structure

Public Structure Bar(Of T)
    Public x As T
End Structure

Public Structure Baz(Of T As Structure)
    Public x As T
End Structure