diff --git a/Octokit.Reactive/Clients/IObservableIssueReactionsClient.cs b/Octokit.Reactive/Clients/IObservableIssueReactionsClient.cs
index ac59227e..829c6997 100644
--- a/Octokit.Reactive/Clients/IObservableIssueReactionsClient.cs
+++ b/Octokit.Reactive/Clients/IObservableIssueReactionsClient.cs
@@ -5,7 +5,7 @@ namespace Octokit.Reactive
     public interface IObservableIssueReactionsClient
     {
         /// <summary>
-        /// Creates a reaction for an specified Commit Comment
+        /// Creates a reaction for an specified Issue.
         /// </summary>
         /// <remarks>https://developer.github.com/v3/reactions/#create-reaction-for-an-issue</remarks>
         /// <param name="owner">The owner of the repository</param>
@@ -16,7 +16,7 @@ namespace Octokit.Reactive
         IObservable<Reaction> Create(string owner, string name, int number, NewReaction reaction);
 
         /// <summary>
-        /// List reactions for a specified Commit Comment
+        /// List reactions for an specified Issue.
         /// </summary>
         /// <remarks>https://developer.github.com/v3/reactions/#list-reactions-for-an-issue</remarks>
         /// <param name="owner">The owner of the repository</param>
diff --git a/Octokit.Tests/Clients/CommitCommentReactionsClientTests.cs b/Octokit.Tests/Clients/CommitCommentReactionsClientTests.cs
index 67750a3e..caffd2fa 100644
--- a/Octokit.Tests/Clients/CommitCommentReactionsClientTests.cs
+++ b/Octokit.Tests/Clients/CommitCommentReactionsClientTests.cs
@@ -39,7 +39,7 @@ namespace Octokit.Tests.Clients
                 await Assert.ThrowsAsync<ArgumentException>(() => client.CommitComment.Create("", "name", 1, new NewReaction(ReactionType.Heart)));
                 await Assert.ThrowsAsync<ArgumentNullException>(() => client.CommitComment.Create("owner", null, 1, new NewReaction(ReactionType.Heart)));
                 await Assert.ThrowsAsync<ArgumentException>(() => client.CommitComment.Create("owner", "", 1, new NewReaction(ReactionType.Heart)));
-                await Assert.ThrowsAsync<ArgumentException>(() => client.CommitComment.Create("owner", "name", 1, null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.CommitComment.Create("owner", "name", 1, null));
             }
         }
 
diff --git a/Octokit.Tests/Clients/IssueCommentReactionsClientTests.cs b/Octokit.Tests/Clients/IssueCommentReactionsClientTests.cs
index 027d3dfe..cc0139e2 100644
--- a/Octokit.Tests/Clients/IssueCommentReactionsClientTests.cs
+++ b/Octokit.Tests/Clients/IssueCommentReactionsClientTests.cs
@@ -39,7 +39,7 @@ namespace Octokit.Tests.Clients
                 await Assert.ThrowsAsync<ArgumentException>(() => client.IssueComment.Create("", "name", 1, new NewReaction(ReactionType.Heart)));
                 await Assert.ThrowsAsync<ArgumentNullException>(() => client.IssueComment.Create("owner", null, 1, new NewReaction(ReactionType.Heart)));
                 await Assert.ThrowsAsync<ArgumentException>(() => client.IssueComment.Create("owner", "", 1, new NewReaction(ReactionType.Heart)));
-                await Assert.ThrowsAsync<ArgumentException>(() => client.IssueComment.Create("owner", "name", 1, null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.IssueComment.Create("owner", "name", 1, null));
             }
         }
 
diff --git a/Octokit.Tests/Clients/IssueReactionsClientTests.cs b/Octokit.Tests/Clients/IssueReactionsClientTests.cs
index d0565b90..fb5c23e7 100644
--- a/Octokit.Tests/Clients/IssueReactionsClientTests.cs
+++ b/Octokit.Tests/Clients/IssueReactionsClientTests.cs
@@ -39,7 +39,7 @@ namespace Octokit.Tests.Clients
                 await Assert.ThrowsAsync<ArgumentException>(() => client.Issue.Create("", "name", 1, new NewReaction(ReactionType.Heart)));
                 await Assert.ThrowsAsync<ArgumentNullException>(() => client.Issue.Create("owner", null, 1, new NewReaction(ReactionType.Heart)));
                 await Assert.ThrowsAsync<ArgumentException>(() => client.Issue.Create("owner", "", 1, new NewReaction(ReactionType.Heart)));
-                await Assert.ThrowsAsync<ArgumentException>(() => client.Issue.Create("owner", "name", 1, null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Issue.Create("owner", "name", 1, null));
             }
         }
 
diff --git a/Octokit.Tests/Clients/PullRequestReviewCommentReactionsClientTests.cs b/Octokit.Tests/Clients/PullRequestReviewCommentReactionsClientTests.cs
index 669b3a94..b2dfc120 100644
--- a/Octokit.Tests/Clients/PullRequestReviewCommentReactionsClientTests.cs
+++ b/Octokit.Tests/Clients/PullRequestReviewCommentReactionsClientTests.cs
@@ -39,7 +39,7 @@ namespace Octokit.Tests.Clients
                 await Assert.ThrowsAsync<ArgumentException>(() => client.PullRequestReviewComment.Create("", "name", 1, new NewReaction(ReactionType.Heart)));
                 await Assert.ThrowsAsync<ArgumentNullException>(() => client.PullRequestReviewComment.Create("owner", null, 1, new NewReaction(ReactionType.Heart)));
                 await Assert.ThrowsAsync<ArgumentException>(() => client.PullRequestReviewComment.Create("owner", "", 1, new NewReaction(ReactionType.Heart)));
-                await Assert.ThrowsAsync<ArgumentException>(() => client.PullRequestReviewComment.Create("owner", "name", 1, null));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.PullRequestReviewComment.Create("owner", "name", 1, null));
             }
         }
 
diff --git a/Octokit.Tests/Reactive/ObservableCommitCommentReactionClientTests.cs b/Octokit.Tests/Reactive/ObservableCommitCommentReactionClientTests.cs
index 794dae4e..2daf811f 100644
--- a/Octokit.Tests/Reactive/ObservableCommitCommentReactionClientTests.cs
+++ b/Octokit.Tests/Reactive/ObservableCommitCommentReactionClientTests.cs
@@ -35,7 +35,7 @@ namespace Octokit.Tests.Reactive
                 Assert.Throws<ArgumentException>(() => _client.CommitComment.Create("", "name", 1, new NewReaction(ReactionType.Heart)));
                 Assert.Throws<ArgumentNullException>(() => _client.CommitComment.Create("owner", null, 1, new NewReaction(ReactionType.Heart)));
                 Assert.Throws<ArgumentException>(() => _client.CommitComment.Create("owner", "", 1, new NewReaction(ReactionType.Heart)));
-                Assert.Throws<ArgumentException>(() => _client.CommitComment.Create("owner", "name", 1, null));
+                Assert.Throws<ArgumentNullException>(() => _client.CommitComment.Create("owner", "name", 1, null));
             }
         }
 
diff --git a/Octokit.Tests/Reactive/ObservablePullRequestReviewCommentReactionsClientTests.cs b/Octokit.Tests/Reactive/ObservablePullRequestReviewCommentReactionsClientTests.cs
index cd85f612..65c0c369 100644
--- a/Octokit.Tests/Reactive/ObservablePullRequestReviewCommentReactionsClientTests.cs
+++ b/Octokit.Tests/Reactive/ObservablePullRequestReviewCommentReactionsClientTests.cs
@@ -35,7 +35,7 @@ namespace Octokit.Tests.Reactive
                 Assert.Throws<ArgumentException>(() => _client.PullRequestReviewComment.Create("", "name", 1, new NewReaction(ReactionType.Heart)));
                 Assert.Throws<ArgumentNullException>(() => _client.PullRequestReviewComment.Create("owner", null, 1, new NewReaction(ReactionType.Heart)));
                 Assert.Throws<ArgumentException>(() => _client.PullRequestReviewComment.Create("owner", "", 1, new NewReaction(ReactionType.Heart)));
-                Assert.Throws<ArgumentException>(() => _client.PullRequestReviewComment.Create("owner", "name", 1, null));
+                Assert.Throws<ArgumentNullException>(() => _client.PullRequestReviewComment.Create("owner", "name", 1, null));
             }
         }
 
diff --git a/Octokit/Clients/IssueReactionsClient.cs b/Octokit/Clients/IssueReactionsClient.cs
index 0ddd8ffc..ecb96c0a 100644
--- a/Octokit/Clients/IssueReactionsClient.cs
+++ b/Octokit/Clients/IssueReactionsClient.cs
@@ -22,8 +22,8 @@ namespace Octokit
         /// <returns></returns>
         public Task<Reaction> Create(string owner, string name, int number, NewReaction reaction)
         {
-            Ensure.ArgumentNotNull(owner, "owner");
-            Ensure.ArgumentNotNull(name, "name");
+            Ensure.ArgumentNotNullOrEmptyString(owner, "owner");
+            Ensure.ArgumentNotNullOrEmptyString(name, "name");
             Ensure.ArgumentNotNull(reaction, "reaction");
 
             return ApiConnection.Post<Reaction>(ApiUrls.IssueReactions(owner, name, number), reaction, AcceptHeaders.ReactionsPreview);
@@ -39,8 +39,8 @@ namespace Octokit
         /// <returns></returns>
         public Task<IReadOnlyList<Reaction>> GetAll(string owner, string name, int number)
         {
-            Ensure.ArgumentNotNull(owner, "owner");
-            Ensure.ArgumentNotNull(name, "name");
+            Ensure.ArgumentNotNullOrEmptyString(owner, "owner");
+            Ensure.ArgumentNotNullOrEmptyString(name, "name");
 
             return ApiConnection.GetAll<Reaction>(ApiUrls.IssueReactions(owner, name, number), AcceptHeaders.ReactionsPreview);
         }