From 06737995ed95fbe6fee65ca967cba106e0ff78f4 Mon Sep 17 00:00:00 2001
From: Brendan Forster <brendan@github.com>
Date: Wed, 27 Nov 2013 12:37:58 -0800
Subject: [PATCH] catch an obscure requirement when creating trees

---
 Octokit.Tests/Clients/TreesClientTests.cs | 13 +++++++++++++
 Octokit/Clients/TreesClient.cs            |  9 ++++++++-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/Octokit.Tests/Clients/TreesClientTests.cs b/Octokit.Tests/Clients/TreesClientTests.cs
index 60a18e2a..28bcc1b4 100644
--- a/Octokit.Tests/Clients/TreesClientTests.cs
+++ b/Octokit.Tests/Clients/TreesClientTests.cs
@@ -62,6 +62,19 @@ namespace Octokit.Tests
                 await AssertEx.Throws<ArgumentNullException>(async () => await client.Create("owner", null, new NewTree()));
                 await AssertEx.Throws<ArgumentException>(async () => await client.Create("owner", "", new NewTree()));
             }
+
+            [Fact]
+            public async Task EnsureExceptionIsThrownWhenModeIsNotProvided()
+            {
+                var newTree = new NewTree();
+                newTree.Tree.Add(new NewTreeItem { Path = "README.md", Type = TreeType.Blob, Sha = "2e1a73d60f004fd842d4bad28aa42392d4f35d28" });
+
+                var connection = Substitute.For<IApiConnection>();
+                var client = new TreesClient(connection);
+
+                await AssertEx.Throws<ArgumentException>(
+                    async () => await client.Create("fake", "repo", newTree));
+            }
         }
 
         public class TheCtor
diff --git a/Octokit/Clients/TreesClient.cs b/Octokit/Clients/TreesClient.cs
index 085ee05a..3d109fa9 100644
--- a/Octokit/Clients/TreesClient.cs
+++ b/Octokit/Clients/TreesClient.cs
@@ -1,4 +1,6 @@
-using System.Threading.Tasks;
+using System;
+using System.Linq;
+using System.Threading.Tasks;
 
 namespace Octokit
 {
@@ -44,6 +46,11 @@ namespace Octokit
             Ensure.ArgumentNotNullOrEmptyString(name, "name");
             Ensure.ArgumentNotNull(newTree, "newTree");
 
+            if (newTree.Tree.Any(t => String.IsNullOrWhiteSpace(t.Mode)))
+            {
+                throw new ArgumentException("You have specified items in the tree which do not have a Mode value set.");
+            }
+
             return ApiConnection.Post<TreeResponse>(ApiUrls.Tree(owner, name), newTree);
         }
     }