Compiler Error CS0845


Updated: July 20, 2015

For the latest documentation on Visual Studio 2017 RC, see Visual Studio 2017 RC Documentation.

An expression tree lambda may not contain a coalescing operator with a null literal left-hand side.

Because null by itself does not have a type, the null coalescing operator cannot operate on it.

To correct this error

  1. Cast the null literal to an object.

The following code generates CS0845:

// cs0845.cs  
using System;  
using System.Linq;  
using System.Linq.Expressions;  
namespace ConsoleApplication1  
    class Program  
        static void Main(string[] args)  
            Expression<Func<object>> e = () => null ?? null; // CS0845  
            // Try the following line instead.  
            // Expression<Func<object>> e = () => (object)null ?? null;