From 3f8b319f54b6b9e145469feeb82778f5015f86a0 Mon Sep 17 00:00:00 2001
From: Doug Bunting <dougbu@microsoft.com>
Date: Thu, 31 Aug 2017 14:42:38 -0700
Subject: [PATCH] Fix `First()` failure when `$(BuildGraphOf)` is set - still
 must build entire Universe locally before using `$(BuildGraphOf)`

---
 build/tasks/CalculateBuildGraph.cs | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/build/tasks/CalculateBuildGraph.cs b/build/tasks/CalculateBuildGraph.cs
index 59e0172ec6..1dc3abfecf 100644
--- a/build/tasks/CalculateBuildGraph.cs
+++ b/build/tasks/CalculateBuildGraph.cs
@@ -50,7 +50,13 @@ namespace RepoTasks
             foreach (var repositoryTaskItem in Repositories)
             {
                 var repositoryName = repositoryTaskItem.ItemSpec;
-                var graphNodeRepository = graph.First(g => g.Repository.Name == repositoryName);
+                var graphNodeRepository = graph.FirstOrDefault(g => g.Repository.Name == repositoryName);
+                if (graphNodeRepository == null)
+                {
+                    // StartGraphAt was specified so the graph is incomplete.
+                    continue;
+                }
+
                 var order = TopologicalSort.GetOrder(graphNodeRepository);
                 repositoryTaskItem.SetMetadata("Order", order.ToString());
                 repositoriesWithOrder.Add((repositoryTaskItem, order));