Optional Test Parameters of string cannot be defaulted to null

[PhillipPruett]

Exception in thrown on MapTestRoutes call.
This very likely is the case for more than just strings.

[ArgumentException: Expression of type 'System.Object' cannot be used for parameter of type 'System.String' of method 'System.Threading.Tasks.Task1[System.Object] CreateCustomClock(System.String)']
System.Linq.Expressions.Expression.ValidateOneArgument(MethodBase method, ExpressionType nodeKind, Expression arg, ParameterInfo pi) +4401680
System.Linq.Expressions.Expression.ValidateArgumentTypes(MethodBase method, ExpressionType nodeKind, ReadOnlyCollection1& arguments) +138 System.Linq.Expressions.Expression.Call(Expression instance, MethodInfo method, IEnumerable1 arguments) +70
Its.Log.Monitoring.TestDefinition1.BuildTestMethodExpression(MethodInfo methodInfo, IEnumerable1 parameters) +213
Its.Log.Monitoring.TestDefinition`1..ctor(MethodInfo methodInfo) +300

[TargetInvocationException: Exception has been thrown by the target of an invocation.]
System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor) +0
System.Reflection.RuntimeConstructorInfo.Invoke(BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture) +243
System.RuntimeType.CreateInstanceImpl(BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes, StackCrawlMark& stackMark) +1065
System.Activator.CreateInstance(Type type, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes) +124
System.Activator.CreateInstance(Type type, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture) +20
Its.Log.Monitoring.TestDefinition.Create(MethodInfo methodInfo) +138
System.Linq.WhereSelectArrayIterator2.MoveNext() +58 System.Linq.<SelectManyIterator>d__162.MoveNext() +227
Its.Log.Monitoring.TestDiscovery.GetTestDefinitions(IEnumerable1 monitoringTests) +341 Its.Log.Monitoring.HttpConfigurationExtensions.MapTestRoutes(HttpConfiguration configuration, Action1 configureTargets, String baseUri, IEnumerable1 testTypes, HttpMessageHandler handler, String testUiScriptUrl, IEnumerable1 testUiLibraryUrls) +754
Microsoft.Datamarket.Monitoring.Web.Startup.Configuration(IAppBuilder app) in C:\Git\monitoring\Monitor.Web\Startup.cs:469

[TargetInvocationException: Exception has been thrown by the target of an invocation.]
System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor) +0
System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments) +92
System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture) +101
System.Reflection.MethodBase.Invoke(Object obj, Object[] parameters) +21
Owin.Loader.<>c__DisplayClass12.b__b(IAppBuilder builder) +77
Owin.Loader.<>c__DisplayClass1.b__0(IAppBuilder builder) +139
Microsoft.Owin.Host.SystemWeb.<>c__DisplayClass2.b__0(IAppBuilder builder) +69
Microsoft.Owin.Host.SystemWeb.OwinAppContext.Initialize(Action1 startup) +546 Microsoft.Owin.Host.SystemWeb.OwinBuilder.Build(Action1 startup) +58
Microsoft.Owin.Host.SystemWeb.OwinHttpModule.InitializeBlueprint() +95
System.Threading.LazyInitializer.EnsureInitializedCore(T& target, Boolean& initialized, Object& syncLock, Func1 valueFactory) +115 System.Threading.LazyInitializer.EnsureInitialized(T& target, Boolean& initialized, Object& syncLock, Func1 valueFactory) +72
Microsoft.Owin.Host.SystemWeb.OwinHttpModule.Init(HttpApplication context) +96
System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr appContext, HttpContext context, MethodInfo[] handlers) +534
System.Web.HttpApplication.InitSpecial(HttpApplicationState state, MethodInfo[] handlers, IntPtr appContext, HttpContext context) +172
System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr appContext, HttpContext context) +339
System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr appContext) +296

[HttpException (0x80004005): Exception has been thrown by the target of an invocation.]
System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +9946132
System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +90
System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +261`