Sort methods on Array, List<T>, and other core collections accept null comparers. This is not the case for immutable collections, despite what the doc comments claim. This change fixes the inconsistency buy allowing null comparers being passed to Sort methods of the immutable collections.
Update ImmutableArray`1+Builder.cs
Merge pull request #140 from KrzysztofCwalina/dotnet1

Allow null comparer to be passed to ImmutableArray<T>.Sort