Return an empty collection when Linq where returns nothing

Question

I am using the below statement with the intent of getting all of the machine objects from the `MachineList` collection (type IEnumerable) that have a `MachineStatus` of i. The `MachineList` collection will not always contain machines with a status of i. At times when no machines have a `MachineStatus` of i I'd like to return an empty collection. My call to `ActiveMachines` (which is used first) works but `InactiveMachines` does not. ``` public IEnumerable ActiveMachines { get { return Customer.MachineList .Where(m => m.MachineStatus == "a"); } } public IEnumerable InactiveMachines { get { return Customer.MachineList .Where(m => m.MachineStatus == "i"); } } ``` Edit Upon further examination it appears that any enumeration of `MachineList` will cause subsequent enumerations of `MachineList` to throw an exeception: `Object reference not set to an instance of an object`. Therefore, it doesn't matter if a call is made to `ActiveMachines` or `InactiveMachines` as its an is…

Accepted Answer

`Where` returns an empty sequence if there are no matches; this is a perfectly valid sequence (not null). The only way you'd get a null is if you call `FirstOrDefault` or `SingleOrDefault`.

Are you sure the bug is where you think it is?

```
int?[] nums = { 1, 3, 5 };
var qry = nums.Where(i => i % 2 == 0);
Console.WriteLine(qry == null); // false
Console.WriteLine(qry.Count()); // 0
var list = qry.ToList();
Console.WriteLine(list.Count); // 0
var first = qry.FirstOrDefault();
Console.WriteLine(first == null); // true
```

Return an empty collection when Linq where returns nothing

Solution

Problem