added tests to catch regression

Octokit.Tests/Helpers/UriExtensionsTests.cs

@@ -22,6 +22,19 @@ namespace Octokit.Tests.Helpers
                 Assert.Equal(new Uri("https://example.com?foo=foo%20val&bar=barval"), uriWithParameters);
             }
 
+            [Fact]
+            public void ThrowsExceptionWhenNullValueProvided()
+            {
+                var uri = new Uri("https://example.com");
+
+                var parameters = new Dictionary<string, string>
+                {
+                    {"foo", null },
+                };
+
+                Assert.Throws<ArgumentNullException>(() => uri.ApplyParameters(parameters));
+            }
+
             [Fact]
             public void AppendsParametersAsQueryStringToRelativeUri()
             {

Octokit.Tests/Models/SearchCodeRequestTests.cs

@@ -1,4 +1,5 @@
-using Octokit;
+using System;
+using Octokit;
 using Octokit.Tests.Helpers;
 using Xunit;
 
@@ -16,5 +17,13 @@ public class SearchCodeRequestTests
             // If I can cast this to a writeable collection, then that defeats the purpose of a read only.
             AssertEx.IsReadOnlyCollection<string>(result);
         }
+
+        [Fact]
+        public void SortNotSpecifiedByDefault()
+        {
+            var request = new SearchCodeRequest("test");
+            Assert.True(String.IsNullOrWhiteSpace(request.Sort));
+            Assert.False(request.Parameters.ContainsKey("sort"));
+        }
     }
 }

Octokit.Tests/Models/SearchIssuesRequestTests.cs

@@ -1,4 +1,5 @@
-using Octokit;
+using System;
+using Octokit;
 using Octokit.Tests.Helpers;
 using Xunit;
 
@@ -16,5 +17,13 @@ internal class SearchIssuesRequestTests
             // If I can cast this to a writeable collection, then that defeats the purpose of a read only.
             AssertEx.IsReadOnlyCollection<string>(result);
         }
+
+        [Fact]
+        public void SortNotSpecifiedByDefault()
+        {
+            var request = new SearchIssuesRequest("test");
+            Assert.True(String.IsNullOrWhiteSpace(request.Sort));
+            Assert.False(request.Parameters.ContainsKey("sort"));
+        }
     }
 }

Octokit.Tests/Models/SearchUsersRequestTests.cs

@@ -1,4 +1,5 @@
-using Octokit;
+using System;
+using Octokit;
 using Octokit.Tests.Helpers;
 using Xunit;
 
@@ -16,5 +17,13 @@ internal class SearchUsersRequestTests
             // If I can cast this to a writeable collection, then that defeats the purpose of a read only.
             AssertEx.IsReadOnlyCollection<string>(result);
         }
+
+        [Fact]
+        public void SortNotSpecifiedByDefault()
+        {
+            var request = new SearchUsersRequest("shiftkey");
+            Assert.True(String.IsNullOrWhiteSpace(request.Sort));
+            Assert.False(request.Parameters.ContainsKey("sort"));
+        }
     }
 }