diff --git a/Octokit.Tests/Models/RepositoryRequestTests.cs b/Octokit.Tests/Models/RepositoryRequestTests.cs
new file mode 100644
index 0000000000..e5d89562fc
--- /dev/null
+++ b/Octokit.Tests/Models/RepositoryRequestTests.cs
@@ -0,0 +1,50 @@
+using Xunit;
+
+namespace Octokit.Tests.Models
+{
+    public class RepositoryRequestTests
+    {
+        public class TheToParametersDictionaryMethod
+        {
+            [Fact]
+            public void ContainsSetValues()
+            {
+                var request = new RepositoryRequest
+                {
+                    Type = RepositoryType.All,
+                    Sort = RepositorySort.FullName,
+                    Direction = SortDirection.Ascending
+                };
+
+                var parameters = request.ToParametersDictionary();
+
+                Assert.Equal(3, parameters.Count);
+                Assert.Equal("all", parameters["type"]);
+                Assert.Equal("full_name", parameters["sort"]);
+                Assert.Equal("asc", parameters["direction"]);
+
+                request = new RepositoryRequest
+                {
+                    Affiliation = RepositoryAffiliation.All,
+                    Visibility = RepositoryVisibility.Public
+                };
+
+                parameters = request.ToParametersDictionary();
+
+                Assert.Equal(2, parameters.Count);
+                Assert.Equal("owner, collaborator, organization_member", parameters["affiliation"]);
+                Assert.Equal("public", parameters["visibility"]);
+            }
+
+            [Fact]
+            public void DoesNotReturnValuesForDefaultRequest()
+            {
+                var request = new RepositoryRequest();
+
+                var parameters = request.ToParametersDictionary();
+
+                Assert.Empty(parameters);
+            }
+        }
+    }
+}
diff --git a/Octokit.Tests/Octokit.Tests.csproj b/Octokit.Tests/Octokit.Tests.csproj
index 99537721eb..5c6484c309 100644
--- a/Octokit.Tests/Octokit.Tests.csproj
+++ b/Octokit.Tests/Octokit.Tests.csproj
@@ -182,6 +182,7 @@
     <Compile Include="Models\PullRequestRequestTests.cs" />
     <Compile Include="Models\PunchCardTests.cs" />
     <Compile Include="Models\ReadOnlyPagedCollectionTests.cs" />
+    <Compile Include="Models\RepositoryRequestTests.cs" />
     <Compile Include="Models\RepositoryUpdateTests.cs" />
     <Compile Include="Models\RequestParametersTests.cs" />
     <Compile Include="Models\SearchCodeRequestTests.cs" />
diff --git a/Octokit/Models/Request/RepositoryRequest.cs b/Octokit/Models/Request/RepositoryRequest.cs
index 1f5d2e8907..03753b432e 100644
--- a/Octokit/Models/Request/RepositoryRequest.cs
+++ b/Octokit/Models/Request/RepositoryRequest.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
@@ -19,7 +20,7 @@ public class RepositoryRequest : RequestParameters
         /// The type.
         /// </value>
         [SuppressMessage("Microsoft.Naming", "CA1721:PropertyNamesShouldNotMatchGetMethods")]
-        public RepositoryType Type { get; set; }
+        public RepositoryType? Type { get; set; }
 
         /// <summary>
         /// Gets or sets the sort property.
@@ -27,7 +28,7 @@ public class RepositoryRequest : RequestParameters
         /// <value>
         /// The sort.
         /// </value>
-        public RepositorySort Sort { get; set; }
+        public RepositorySort? Sort { get; set; }
 
         /// <summary>
         /// Gets or sets the sort direction.
@@ -35,7 +36,7 @@ public class RepositoryRequest : RequestParameters
         /// <value>
         /// The direction.
         /// </value>
-        public SortDirection Direction { get; set; }
+        public SortDirection? Direction { get; set; }
 
         /// <summary>
         /// Gets or sets the visibility property.
@@ -43,7 +44,7 @@ public class RepositoryRequest : RequestParameters
         /// <value>
         ///  The visibility.
         /// </value>
-        public RepositoryVisibility Visibility { get; set; }
+        public RepositoryVisibility? Visibility { get; set; }
 
         /// <summary>
         /// Gets or sets the affiliation property.
@@ -51,13 +52,25 @@ public class RepositoryRequest : RequestParameters
         /// <value>
         ///  The affiliation.
         /// </value>
-        public RepositoryAffiliation Affiliation { get; set; }
+        public RepositoryAffiliation? Affiliation { get; set; }
 
         internal string DebuggerDisplay
         {
             get
             {
-                return string.Format(CultureInfo.InvariantCulture, "Type: {0}, Sort: {1}, Direction: {2}", Type, Sort, Direction);
+                var propValues = new List<string>();
+                if (Type.HasValue)
+                    propValues.Add(string.Format(CultureInfo.InvariantCulture, "Type: {0}", Type));
+                if (Sort.HasValue)
+                    propValues.Add(string.Format(CultureInfo.InvariantCulture, "Sort: {0}", Sort));
+                if (Direction.HasValue)
+                    propValues.Add(string.Format(CultureInfo.InvariantCulture, "Direction: {0}", Direction));
+                if (Visibility.HasValue)
+                    propValues.Add(string.Format(CultureInfo.InvariantCulture, "Visibility: {0}", Visibility));
+                if (Affiliation.HasValue)
+                    propValues.Add(string.Format(CultureInfo.InvariantCulture, "Affiliation: {0}", Affiliation));
+
+                return string.Join(", ", propValues);
             }
         }
     }
diff --git a/Octokit/Models/Request/RequestParameters.cs b/Octokit/Models/Request/RequestParameters.cs
index fa689f8c76..ccd7121ca9 100644
--- a/Octokit/Models/Request/RequestParameters.cs
+++ b/Octokit/Models/Request/RequestParameters.cs
@@ -49,6 +49,9 @@ static List<PropertyParameter> GetPropertyParametersForType(Type type)
             Justification = "GitHub API depends on lower case strings")]
         static Func<PropertyInfo, object, string> GetValueFunc(Type propertyType)
         {
+            // get underlying type if nullable
+            propertyType = Nullable.GetUnderlyingType(propertyType) ?? propertyType;
+
             if (typeof(IEnumerable<string>).IsAssignableFrom(propertyType))
             {
                 return (prop, value) =>