CS8107 Feature 'nullable reference types' is not available in C# 7.0. Please use language version 8.0 or greater

[vsfeedback]

This error reported for this sequence of code

    public static byte[] ConvertToByteArray(object value)
    {
        return
            value is byte[] ? (byte[])value :
            value == null ? null :
                Util.Convert.ToByteArray(value);
    }

This issue has been moved from https://developercommunity.visualstudio.com/content/problem/400852/cs8107-feature-nullable-reference-types-is-not-ava.html
VSTS ticketId: 742071
These are the original issue comments:

Alexey Kuznetsov on 12/7/2018, 01:15 AM (3 days ago): The similar problem.The code the something like that:object value = new string[0];object resultValue = value is string[]? value as string[] : new[] { value.ToString() };Lang c#7. Works in VS 2017.
These are the original issue solutions:
(no solutions)

[jaredpar]

@cston isn't this a dupe of the conditional parsing bug you fixed for preview 2?

[cston]

@jaredpar, yes this is the parsing bug fixed in #31050.