From 4d662695ba402e2457969b0d65b17985abec35bf Mon Sep 17 00:00:00 2001
From: ujwalakhaire <ujwala.khaire@gmail.com>
Date: Fri, 4 May 2018 15:36:05 -0700
Subject: [PATCH] Bugfix/handle empty stack (#4549)

* Added a check for count before poping from stack.

* Fixed test to reflect actual expected exception.
---
 CSharp/Library/Microsoft.Bot.Builder/Fibers/Fiber.cs   | 6 +++++-
 CSharp/Tests/Microsoft.Bot.Builder.Tests/FiberTests.cs | 2 +-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/CSharp/Library/Microsoft.Bot.Builder/Fibers/Fiber.cs b/CSharp/Library/Microsoft.Bot.Builder/Fibers/Fiber.cs
index d182b7e64e..9b1132cbb5 100644
--- a/CSharp/Library/Microsoft.Bot.Builder/Fibers/Fiber.cs
+++ b/CSharp/Library/Microsoft.Bot.Builder/Fibers/Fiber.cs
@@ -234,7 +234,11 @@ async Task<IWait<C>> IFiberLoop<C>.PollAsync(C context, CancellationToken token)
                 }
                 catch (Exception error)
                 {
-                    this.stack.Pop();
+                    if (this.stack.Count != 0)
+                    {
+                        this.stack.Pop();
+                    }
+
                     if (this.stack.Count == 0)
                     {
                         throw;
diff --git a/CSharp/Tests/Microsoft.Bot.Builder.Tests/FiberTests.cs b/CSharp/Tests/Microsoft.Bot.Builder.Tests/FiberTests.cs
index 46df23ed46..cdf30a2330 100644
--- a/CSharp/Tests/Microsoft.Bot.Builder.Tests/FiberTests.cs
+++ b/CSharp/Tests/Microsoft.Bot.Builder.Tests/FiberTests.cs
@@ -330,7 +330,7 @@ public async Task Fiber_OneCall_NeedDone()
         }
 
         [TestMethod]
-        [ExpectedException(typeof(InvalidOperationException))]
+        [ExpectedException(typeof(InvalidNeedException))]
         public async Task Fiber_OneCall_ThenDone_Throws()
         {
             // arrange