roslyn: VB.NET ".?" Syntax OR GreaterThan Breaking Change

Version Used: Somewhere between the version in msbuild 16.1 and 16.7

Steps to Reproduce:

Code example:

Sub Main()

        Dim map As Map = Nothing

        Console.WriteLine($"1 (Expect Empty): {IsHit(map, 0, 0)}")

        map = New Map() With {.Positions = Nothing}

        Console.WriteLine($"2 (Expect Empty): {IsHit(map, 0, 0)}")

        map = New Map() With {.Positions = New List(Of List(Of String))()}
        map.Positions.Add(Nothing)

        Console.WriteLine($"3 (Expect Empty): {IsHit(map, 0, 0)}")

        map = New Map() With {.Positions = New List(Of List(Of String))()}
        map.Positions.Add(New List(Of String)())
        map.Positions(0).Add(Nothing)

        Console.WriteLine($"4 (Expect Empty): {IsHit(map, 0, 0)}")

        map = New Map() With {.Positions = New List(Of List(Of String))()}
        map.Positions.Add(New List(Of String)())
        map.Positions(0).Add("")

        Console.WriteLine($"5 (Expect Miss): {IsHit(map, 0, 0)}")

        map = New Map() With {.Positions = New List(Of List(Of String))()}
        map.Positions.Add(New List(Of String)())
        map.Positions(0).Add("X")

        Console.WriteLine($"6 (Expect Hit): {IsHit(map, 0, 0)}")

        Console.ReadLine()

    End Sub

    Function IsHit(map As Map, x As Integer, y As Integer) As String

        Try
            If map?.Positions?.Count() > x AndAlso map.Positions(x)?.Count() > y AndAlso Not map.Positions(x)(y) Is Nothing Then

                If map.Positions(x)(y).Equals("X", StringComparison.InvariantCultureIgnoreCase) Then
                    Return "Hit"
                Else
                    Return "Miss"
                End If
            Else
                Return "Empty"
            End If
        Catch ex As Exception
            Return $"Error - {ex.Message}"
        End Try

    End Function

    Class Map

        Public Property Positions As List(Of List(Of String))

    End Class

Expected Behavior:

Output:

1 (Expect Empty): Empty
2 (Expect Empty): Empty
3 (Expect Empty): Empty
4 (Expect Empty): Empty
5 (Expect Miss): Miss
6 (Expect Hit): Hit

Actual Behavior:

Output:

1 (Expect Empty): Error - Object reference not set to an instance of an object.
2 (Expect Empty): Error - Object reference not set to an instance of an object.
3 (Expect Empty): Error - Object reference not set to an instance of an object.
4 (Expect Empty): Empty
5 (Expect Miss): Miss
6 (Expect Hit): Hit

When running code compiled using an older version of the compiler, the map?.Positions?.Count() > x AndAlso map.Positions(x)?.Count() > y AndAlso Not map.Positions(x)(y) Is Nothing If check will return False and the output is as expected. However, on newer versions, this same if will throw a null reference exception.