diff --git a/Octokit/Models/Request/RepositoryRequest.cs b/Octokit/Models/Request/RepositoryRequest.cs
index 1f5d2e89..aae2b897 100644
--- a/Octokit/Models/Request/RepositoryRequest.cs
+++ b/Octokit/Models/Request/RepositoryRequest.cs
@@ -125,6 +125,12 @@ namespace Octokit
     /// </summary>
     public enum RepositoryVisibility
     {
+        /// <summary>
+        /// Default value (all)
+        /// </summary>
+        [Parameter(Value = "")]
+        Default,
+
         /// <summary>
         /// Returns only public repositories
         /// </summary>     
@@ -146,6 +152,12 @@ namespace Octokit
     /// </summary>
     public enum RepositoryAffiliation
     {
+        /// <summary>
+        /// Default value (all)
+        /// </summary>
+        [Parameter(Value = "")]
+        Default,
+
         /// <summary>
         /// Repositories that are owned by the authenticated user
         /// </summary>
diff --git a/Octokit/Models/Request/RequestParameters.cs b/Octokit/Models/Request/RequestParameters.cs
index fa689f8c..4fe403f2 100644
--- a/Octokit/Models/Request/RequestParameters.cs
+++ b/Octokit/Models/Request/RequestParameters.cs
@@ -33,7 +33,7 @@ namespace Octokit
             return (from property in map
                     let value = property.GetValue(this)
                     let key = property.Key
-                    where value != null
+                    where !String.IsNullOrEmpty(value)
                     select new { key, value }).ToDictionary(kvp => kvp.key, kvp => kvp.value);
         }