Why does .NET foreach loop throw NullRefException when collection is null?

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So I frequently run into this situation… where Do.Something(...) returns a null collection, like so:

int[] returnArray = Do.Something(...);

Then, I try to use this collection like so:

foreach (int i in returnArray)
{
    // do some more stuff
}

I’m just curious, why can’t a foreach loop operate on a null collection? It seems logical to me that 0 iterations would get executed with a null collection… instead it throws a NullReferenceException. Anyone know why this could be?

This is annoying as I’m working with APIs that aren’t clear on exactly what they return, so I end up with if (someCollection != null) everywhere…

Edit: Thank you all for explaining that foreach uses GetEnumerator and if there is no enumerator to get, the foreach would fail. I guess I’m asking why the language/runtime can’t or won’t do a null check before grabbing the enumerator. It seems to me that the behavior would still be well defined.

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