diff --git a/Octokit.Reactive/Clients/ObservableAuthorizationsClient.cs b/Octokit.Reactive/Clients/ObservableAuthorizationsClient.cs
index 62589d8d..df061785 100644
--- a/Octokit.Reactive/Clients/ObservableAuthorizationsClient.cs
+++ b/Octokit.Reactive/Clients/ObservableAuthorizationsClient.cs
@@ -28,11 +28,15 @@ namespace Octokit.Reactive.Clients
 
         public IObservable<Authorization> Update(long id, AuthorizationUpdate authorization)
         {
+            Ensure.ArgumentNotNull(authorization, "authorization");
+
             return client.Update(id, authorization).ToObservable();
         }
 
         public IObservable<Authorization> Create(AuthorizationUpdate authorization)
         {
+            Ensure.ArgumentNotNull(authorization, "authorization");
+
             return client.Create(authorization).ToObservable();
         }
 
diff --git a/Octokit.Reactive/Clients/ObservableOrganizationsClient.cs b/Octokit.Reactive/Clients/ObservableOrganizationsClient.cs
index a556b06f..3c81cc64 100644
--- a/Octokit.Reactive/Clients/ObservableOrganizationsClient.cs
+++ b/Octokit.Reactive/Clients/ObservableOrganizationsClient.cs
@@ -17,6 +17,8 @@ namespace Octokit.Reactive.Clients
 
         public IObservable<Organization> Get(string org)
         {
+            Ensure.ArgumentNotNullOrEmptyString(org, "org");
+
             return client.Get(org).ToObservable();
         }
 
@@ -27,6 +29,8 @@ namespace Octokit.Reactive.Clients
 
         public IObservable<IReadOnlyCollection<Organization>> GetAll(string user)
         {
+            Ensure.ArgumentNotNullOrEmptyString(user, "user");
+
             return client.GetAll(user).ToObservable();
         }
     }
diff --git a/Octokit.Reactive/Clients/ObservableRepositoriesClient.cs b/Octokit.Reactive/Clients/ObservableRepositoriesClient.cs
index 5463f789..ffa04059 100644
--- a/Octokit.Reactive/Clients/ObservableRepositoriesClient.cs
+++ b/Octokit.Reactive/Clients/ObservableRepositoriesClient.cs
@@ -17,6 +17,9 @@ namespace Octokit.Reactive.Clients
 
         public IObservable<Repository> Get(string owner, string name)
         {
+            Ensure.ArgumentNotNullOrEmptyString(owner, "owner");
+            Ensure.ArgumentNotNullOrEmptyString(name, "name");
+
             return client.Get(owner, name).ToObservable();
         }
 
@@ -27,16 +30,23 @@ namespace Octokit.Reactive.Clients
 
         public IObservable<IReadOnlyCollection<Repository>> GetAllForUser(string login)
         {
+            Ensure.ArgumentNotNullOrEmptyString(login, "login");
+
             return client.GetAllForUser(login).ToObservable();
         }
 
         public IObservable<IReadOnlyCollection<Repository>> GetAllForOrg(string organization)
         {
+            Ensure.ArgumentNotNullOrEmptyString(organization, "organization");
+
             return client.GetAllForOrg(organization).ToObservable();
         }
 
         public IObservable<Readme> GetReadme(string owner, string name)
         {
+            Ensure.ArgumentNotNullOrEmptyString(owner, "owner");
+            Ensure.ArgumentNotNullOrEmptyString(name, "name");
+
             return client.GetReadme(owner, name).ToObservable();
         }
     }
diff --git a/Octokit.Reactive/Clients/ObservableSshKeysClient.cs b/Octokit.Reactive/Clients/ObservableSshKeysClient.cs
index 3ca33f80..9127daaf 100644
--- a/Octokit.Reactive/Clients/ObservableSshKeysClient.cs
+++ b/Octokit.Reactive/Clients/ObservableSshKeysClient.cs
@@ -23,6 +23,8 @@ namespace Octokit.Reactive.Clients
 
         public IObservable<IReadOnlyCollection<SshKey>> GetAll(string user)
         {
+            Ensure.ArgumentNotNullOrEmptyString(user, "user");
+
             return client.GetAll(user).ToObservable();
         }
 
@@ -33,11 +35,15 @@ namespace Octokit.Reactive.Clients
 
         public IObservable<SshKey> Create(SshKeyUpdate key)
         {
+            Ensure.ArgumentNotNull(key, "key");
+
             return client.Create(key).ToObservable();
         }
 
         public IObservable<SshKey> Update(long id, SshKeyUpdate key)
         {
+            Ensure.ArgumentNotNull(key, "key");
+
             return client.Update(id, key).ToObservable();
         }
 
diff --git a/Octokit.Reactive/Clients/ObservableUsersClient.cs b/Octokit.Reactive/Clients/ObservableUsersClient.cs
index 3325ca2b..cefb3dcb 100644
--- a/Octokit.Reactive/Clients/ObservableUsersClient.cs
+++ b/Octokit.Reactive/Clients/ObservableUsersClient.cs
@@ -16,6 +16,8 @@ namespace Octokit.Reactive.Clients
 
         public IObservable<User> Get(string login)
         {
+            Ensure.ArgumentNotNull(login, "login");
+
             return client.Get(login).ToObservable();
         }
 
@@ -26,6 +28,8 @@ namespace Octokit.Reactive.Clients
 
         public IObservable<User> Update(UserUpdate user)
         {
+            Ensure.ArgumentNotNull(user, "user");
+
             return client.Update(user).ToObservable();
         }
     }
diff --git a/Octokit.Reactive/ObservableExtensions.cs b/Octokit.Reactive/ObservableExtensions.cs
index 45a3bd13..bc2e582a 100644
--- a/Octokit.Reactive/ObservableExtensions.cs
+++ b/Octokit.Reactive/ObservableExtensions.cs
@@ -10,6 +10,10 @@ namespace Octokit.Reactive
             string owner,
             string name)
         {
+            Ensure.ArgumentNotNull(client, "client");
+            Ensure.ArgumentNotNullOrEmptyString(owner, "owner");
+            Ensure.ArgumentNotNullOrEmptyString(name, "name");
+
             return client.GetReadme(owner, name).SelectMany(r => r.GetHtmlContent().ToObservable());
         }
     }
diff --git a/Octokit.Reactive/Octokit.Reactive.csproj b/Octokit.Reactive/Octokit.Reactive.csproj
index bd5a1969..48f692c6 100644
--- a/Octokit.Reactive/Octokit.Reactive.csproj
+++ b/Octokit.Reactive/Octokit.Reactive.csproj
@@ -83,6 +83,11 @@
   <ItemGroup>
     <None Include="packages.config" />
   </ItemGroup>
+  <ItemGroup>
+    <CodeAnalysisDictionary Include="..\CustomDictionary.xml">
+      <Link>CustomDictionary.xml</Link>
+    </CodeAnalysisDictionary>
+  </ItemGroup>
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
   <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
        Other similar extension points exist, see Microsoft.Common.targets.
diff --git a/Octokit/Clients/ApiPagination.cs b/Octokit/Clients/ApiPagination.cs
index c3fbfe45..997d9a13 100644
--- a/Octokit/Clients/ApiPagination.cs
+++ b/Octokit/Clients/ApiPagination.cs
@@ -16,6 +16,8 @@ namespace Octokit.Clients
     {
         public async Task<IReadOnlyCollection<T>> GetAllPages(Func<Task<IReadOnlyPagedCollection<T>>> getFirstPage)
         {
+            Ensure.ArgumentNotNull(getFirstPage, "getFirstPage");
+
             var page = await getFirstPage();
             var allItems = new List<T>(page);
             while ((page = await page.GetNextPage()) != null)
diff --git a/Octokit/Clients/AuthorizationsClient.cs b/Octokit/Clients/AuthorizationsClient.cs
index 8f284b6f..9e4bfc17 100644
--- a/Octokit/Clients/AuthorizationsClient.cs
+++ b/Octokit/Clients/AuthorizationsClient.cs
@@ -41,6 +41,8 @@ namespace Octokit.Clients
         /// <returns></returns>
         public async Task<Authorization> Update(long id, AuthorizationUpdate authorization)
         {
+            Ensure.ArgumentNotNull(authorization, "authorization");
+
             var endpoint = "/authorizations/{0}".FormatUri(id);
             return await Client.Update(endpoint, authorization);
         }
@@ -52,6 +54,8 @@ namespace Octokit.Clients
         /// <returns></returns>
         public async Task<Authorization> Create(AuthorizationUpdate authorization)
         {
+            Ensure.ArgumentNotNull(authorization, "authorization");
+
             return await Client.Create(authorizationsEndpoint, authorization);
         }
 
diff --git a/Octokit/Clients/OrganizationsClient.cs b/Octokit/Clients/OrganizationsClient.cs
index 33a87cbc..dc5f8f71 100644
--- a/Octokit/Clients/OrganizationsClient.cs
+++ b/Octokit/Clients/OrganizationsClient.cs
@@ -28,7 +28,7 @@ namespace Octokit.Clients
 
         public async Task<IReadOnlyCollection<Organization>> GetAll(string user)
         {
-            Ensure.ArgumentNotNull(user, "user");
+            Ensure.ArgumentNotNullOrEmptyString(user, "user");
 
             var endpoint = "/users/{0}/orgs".FormatUri(user);
 
diff --git a/Octokit/Clients/RepositoriesClient.cs b/Octokit/Clients/RepositoriesClient.cs
index 12b1c0bb..934fd6ea 100644
--- a/Octokit/Clients/RepositoriesClient.cs
+++ b/Octokit/Clients/RepositoriesClient.cs
@@ -28,7 +28,7 @@ namespace Octokit.Clients
 
         public async Task<IReadOnlyCollection<Repository>> GetAllForUser(string login)
         {
-            Ensure.ArgumentNotNull(login, "login");
+            Ensure.ArgumentNotNullOrEmptyString(login, "login");
 
             var endpoint = "/users/{0}/repos".FormatUri(login);
             
@@ -37,7 +37,7 @@ namespace Octokit.Clients
 
         public async Task<IReadOnlyCollection<Repository>> GetAllForOrg(string organization)
         {
-            Ensure.ArgumentNotNull(organization, "organization");
+            Ensure.ArgumentNotNullOrEmptyString(organization, "organization");
 
             var endpoint = "/orgs/{0}/repos".FormatUri(organization);
             
diff --git a/Octokit/Clients/SshKeysClient.cs b/Octokit/Clients/SshKeysClient.cs
index b36405a8..db9a28a7 100644
--- a/Octokit/Clients/SshKeysClient.cs
+++ b/Octokit/Clients/SshKeysClient.cs
@@ -20,6 +20,8 @@ namespace Octokit.Clients
 
         public async Task<IReadOnlyCollection<SshKey>> GetAll(string user)
         {
+            Ensure.ArgumentNotNullOrEmptyString(user, "user");
+
             var endpoint = "/users/{0}/keys".FormatUri(user);
 
             return await Client.GetAll(endpoint);
diff --git a/Octokit/Helpers/CollectionExtensions.cs b/Octokit/Helpers/CollectionExtensions.cs
index eaf7d585..15cc101b 100644
--- a/Octokit/Helpers/CollectionExtensions.cs
+++ b/Octokit/Helpers/CollectionExtensions.cs
@@ -6,6 +6,8 @@ namespace Octokit
     {
         public static TValue SafeGet<TKey, TValue>(this IReadOnlyDictionary<TKey, TValue> dictionary, TKey key)
         {
+            Ensure.ArgumentNotNull(dictionary, "dictionary");
+
             TValue value;
             return dictionary.TryGetValue(key, out value) ? value : default(TValue);
         }
diff --git a/Octokit/Helpers/StringExtensions.cs b/Octokit/Helpers/StringExtensions.cs
index 0082a9e1..7abaf279 100644
--- a/Octokit/Helpers/StringExtensions.cs
+++ b/Octokit/Helpers/StringExtensions.cs
@@ -19,6 +19,8 @@ namespace Octokit
 
         public static Uri FormatUri(this string pattern, params object[] args)
         {
+            Ensure.ArgumentNotNullOrEmptyString(pattern, "pattern");
+
             return new Uri(string.Format(CultureInfo.InvariantCulture, pattern, args), UriKind.Relative);
         }
 
diff --git a/Octokit/Http/ApiConnection.cs b/Octokit/Http/ApiConnection.cs
index 1042b508..65b6a383 100644
--- a/Octokit/Http/ApiConnection.cs
+++ b/Octokit/Http/ApiConnection.cs
@@ -26,28 +26,39 @@ namespace Octokit.Http
 
         public async Task<T> Get(Uri endpoint)
         {
+            Ensure.ArgumentNotNull(endpoint, "endpoint");
+
             return await GetItem<T>(endpoint);
         }
 
         public async Task<TOther> GetItem<TOther>(Uri endpoint)
         {
+            Ensure.ArgumentNotNull(endpoint, "endpoint");
+
             var response = await Connection.GetAsync<TOther>(endpoint);
             return response.BodyAsObject;
         }
 
         public async Task<string> GetHtml(Uri endpoint)
         {
+            Ensure.ArgumentNotNull(endpoint, "endpoint");
+
             var response = await Connection.GetHtml(endpoint);
             return response.Body;
         }
 
         public async Task<IReadOnlyCollection<T>> GetAll(Uri endpoint)
         {
+            Ensure.ArgumentNotNull(endpoint, "endpoint");
+
             return await pagination.GetAllPages(async () => await GetPage(endpoint));
         }
 
         public async Task<T> Create(Uri endpoint, object data)
         {
+            Ensure.ArgumentNotNull(endpoint, "endpoint");
+            Ensure.ArgumentNotNull(data, "data");
+
             var response = await Connection.PostAsync<T>(endpoint, data);
 
             return response.BodyAsObject;
@@ -55,6 +66,9 @@ namespace Octokit.Http
 
         public async Task<T> Update(Uri endpoint, object data)
         {
+            Ensure.ArgumentNotNull(endpoint, "endpoint");
+            Ensure.ArgumentNotNull(data, "data");
+
             var response = await Connection.PatchAsync<T>(endpoint, data);
 
             return response.BodyAsObject;
@@ -62,11 +76,15 @@ namespace Octokit.Http
 
         public async Task Delete(Uri endpoint)
         {
+            Ensure.ArgumentNotNull(endpoint, "endpoint");
+            
             await Connection.DeleteAsync<T>(endpoint);
         }
 
         async Task<IReadOnlyPagedCollection<T>> GetPage(Uri endpoint)
         {
+            Ensure.ArgumentNotNull(endpoint, "endpoint");
+
             var response = await Connection.GetAsync<List<T>>(endpoint);
             return new ReadOnlyPagedCollection<T>(response, Connection);
         }
diff --git a/Octokit/Http/Connection.cs b/Octokit/Http/Connection.cs
index f45d4d11..e80256cc 100644
--- a/Octokit/Http/Connection.cs
+++ b/Octokit/Http/Connection.cs
@@ -42,6 +42,7 @@ namespace Octokit.Http
             Ensure.ArgumentNotNull(credentialStore, "credentialStore");
             Ensure.ArgumentNotNull(httpClient, "httpClient");
             Ensure.ArgumentNotNull(serializer, "serializer");
+
             if (!baseAddress.IsAbsoluteUri)
             {
                 throw new ArgumentException(
@@ -58,6 +59,8 @@ namespace Octokit.Http
 
         public async Task<IResponse<T>> GetAsync<T>(Uri endpoint)
         {
+            Ensure.ArgumentNotNull(endpoint, "endpoint");
+
             return await Run<T>(new Request
             {
                 Method = HttpMethod.Get,
@@ -68,6 +71,8 @@ namespace Octokit.Http
 
         public async Task<IResponse<string>> GetHtml(Uri endpoint)
         {
+            Ensure.ArgumentNotNull(endpoint, "endpoint");
+
             return await GetHtml(new Request
             {
                 Method = HttpMethod.Get,
@@ -78,6 +83,9 @@ namespace Octokit.Http
 
         public async Task<IResponse<T>> PatchAsync<T>(Uri endpoint, object body)
         {
+            Ensure.ArgumentNotNull(endpoint, "endpoint");
+            Ensure.ArgumentNotNull(body, "body");
+
             return await Run<T>(new Request
             {
                 Method = HttpVerb.Patch,
@@ -89,6 +97,9 @@ namespace Octokit.Http
 
         public async Task<IResponse<T>> PostAsync<T>(Uri endpoint, object body)
         {
+            Ensure.ArgumentNotNull(endpoint, "endpoint");
+            Ensure.ArgumentNotNull(body, "body");
+
             return await Run<T>(new Request
             {
                 Method = HttpMethod.Post,
@@ -100,6 +111,8 @@ namespace Octokit.Http
 
         public async Task DeleteAsync<T>(Uri endpoint)
         {
+            Ensure.ArgumentNotNull(endpoint, "endpoint");
+            
             await Run<T>(new Request
             {
                 Method = HttpMethod.Delete,
diff --git a/Octokit/Http/HttpClientAdapter.cs b/Octokit/Http/HttpClientAdapter.cs
index accdc921..b327c7ad 100644
--- a/Octokit/Http/HttpClientAdapter.cs
+++ b/Octokit/Http/HttpClientAdapter.cs
@@ -24,6 +24,8 @@ namespace Octokit.Http
 
         protected async virtual Task<IResponse<T>> BuildResponse<T>(HttpResponseMessage responseMessage)
         {
+            Ensure.ArgumentNotNull(responseMessage, "responseMessage");
+            
             var response = new ApiResponse<T>
             {
                 Body = await responseMessage
@@ -71,6 +73,8 @@ namespace Octokit.Http
     {
         public static HttpResponseMessage EnsureSuccess(this HttpResponseMessage response)
         {
+            Ensure.ArgumentNotNull(response, "response");
+
             if (response.IsSuccessStatusCode)
             {
                 return response;