What happens to C# Dictionary lookup if the key does not exist?

Question

I tried checking for null but the compiler warns that this condition will never occur. What should I be looking for?

Answer 1

If you're just checking before trying to add a new value, use the ContainsKey method:

if (!openWith.ContainsKey("ht"))
{
    openWith.Add("ht", "hypertrm.exe");
}

If you're checking that the value exists, use the TryGetValue method as described in Jon Skeet's answer.