RCS1166 doesn't work if first operand is null

[cbersch]

The following code should both raise an RCS1166 diagnostic, but the null == a isn't recognized. Tested with 4.14.1

public static class Class1
{
    public static bool Correct(ImmutableArray<int> a)
    {
        return a == null;
    }

    public static bool Wrong(ImmutableArray<int> a)
    {
        return null == a;
    }
}

Until now I couldn't reproduce this with any other custom type, which wouldn't also trigger CS8073.