The example you were quoting from uses LINQ to Objects, where the implicit lambda expressions in the query are converted into delegates… whereas you’re using EF or similar, with IQueryable<T>
queryies, where the lambda expressions are converted into expression trees. Expression trees don’t support the null conditional operator (or tuples).
Just do it the old way:
price = co == null ? 0 : (co.price ?? 0)
(I believe the null-coalescing operator is fine in an expression tree.)