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
Replace '? :' operator with '??'
Merge pull request #160 from LukaszWolanin/master

Replace '? :' operator with '??'
Adding more direct link to the .NET Foundation Forums
Merge pull request #167 from Petermarcu/forum_link

Adding more direct link to the .NET Foundation Forums
Reduce Node sizes by shrinking "height" from Int32 to Byte
Merge pull request #168 from stephentoub/immutable_node_size

Reduce Node sizes by shrinking "height" from Int32 to Byte
Merge branch 'master' of https://github.com/dotnet/corefx