Missing Contracts on Libraries

Question

(Update: please start a new thread for each request. This thread is too long.)

If you are using the static contract checker, one of the main issues you are likely going to run into are missing postconditions on library methods you are calling.

We are working on filling in gaps as fast as we can, but it is mainly driven by us or you finding where important gaps are. Ideally, we would go systematically through the libraries and annotate them. At the moment we don't have the man power.

Please tell us where you find missing contracts and we'll get them in as quickly as we can.

Also, here's a tip you can use to get you unstuck on a small number of missing contracts. I'm not advertising it as a general fix, just a work around to get that last few warnings out.

Say you are making a call in your code arg0.M(arg1,..., argn) where M is missing contracts. Just use the refactoring to extract a method for arg0.M(arg1,..., argn), ideally a static method taking exactly these parameters.

Then write the contracts on your extracted method and call the real method as follows:

T Wrapper(T0 x0, ... Tn xn) {

Contract.Requires(...);

...

Contract.Ensures( <missing post condition> );

var result = x0.M(x1,..,xn);

Contract.Assume( <missing post condition on result>);

return result;

}

The Contract.Assume simply tells the checker that the ensures is missing on M, but that we should now assume it. Of course, the factoring only makes sense if you are calling this method multiple times. Otherwise, you can just put the Assume after you call the original method.

---

Cheers, -MaF (Manuel Fahndrich)

Answer 1

decimal would be great! Thanks

Answer 2

Dispatcher please!!!

Answer 3

I'd like to have contracts for the Linq extensions (e.g. Reverse). Is there a way to view the existing Contracts for the libraries?

- Raphael

Answer 4

Hi Raphael,

You can use reflector to open the *.contract.dll that ship with Code Contract to see which Contracts are available (which is actually a good way to study some real-world contracts examples)

Victor

Answer 5

Enumerable.Select should be marked [Pure].  I guess MS decided otherwise because the selector delegate can have side effects, but Enumerable.Sum is marked [Pure] and has the same issue.

Answer 6

Here are my pain points.

 

CompositionContainer (specifically GetExportedValue never returns null)

ServiceBase (EventLog never returns null) [Done]

ServiceEndpoint

ServiceDescription

ServiceEndpointsCollection

ClientBase<> (Channel never returns null)

EndpointAddess

Assembly (specifically LoadFrom)

X509Certificate

ClientRuntime

SyncronizedCollection<>

DispatchRuntime

EndpointDispatcher

 

Thanks,

Mike

Answer 7

Hi MaF,

Please add the following contracts.

System.Diagnostics:

TraceSource.Switch
    Contract.Ensures(Contract.Result<SourceSwitch>() != null>

ASP.NET:

IBindableTemplate.ExtractValues
    Contract.Requires(container != null);
    Contract.Ensures(Contract.ForAll(Contract.Result<IOrderedDictionary>().Cast<DictionaryEntry>(), e => e.Key != null))

Control.EnsureChildControls
    Contract.Ensures(ChildControlsCreated)

Ensuring ChildControlsCreated makes it possible to define invariants such as the following in pages and user controls so that all of the designer-generated fields are considered non-null by the static checker.  Please let me know if there's a better solution.

[ContractInvariantMethod]
void ObjectInvariant()
{
 Contract.Invariant(!ChildControlsCreated || label != null);
}

void DoSomething()
{
 EnsureChildControls();

 Contract.Assert(label != null);
}

- Dave

---

http://davesexton.com/blog

Answer 8

Hi,

Please also add Contract.Ensures(!ChildControlsCreated) in the constructors for Control and all derived types.

Edit: Or convince the ASP.NET team to add a breaking change and make this property read-only ;)

- Dave

---

http://davesexton.com/blog

Answer 9

Looks like Enumerable.Select's are marked with Pure. What particular method do you have in mind?

---

Cheers, -MaF (Manuel Fahndrich)

Answer 10

Looks like Enumerable.Select's are marked with Pure. What particular method do you have in mind?

Yes, Select is marked with Pure in the current version. I was running 1.4.30601.2.

Thanks,
Bruno

Answer 11

Could you please make an mscorlib.dll/System.Windows.Forms.dll/System.Xml.dll assemblies for 2.0 framework as well? (I assume they would just contain a subset of 4.0/3.5 types, so it won't be that much work)

We're developing an application for which the 2.0 features are pretty much sufficient, so we support the clients with XP and .NET 2.0, but the absense of stdlib contracts makes code somewhat verbose.

 

Answer 12

We use Unity heavily, so IUnityContainer would be very helpful.

 

Answer 13

Count me in with mike's list of ServiceModel classes (and add ChannelFactory <>). Also, is it possible to specify our own contracts for the BCL? I have previously been able to create contracts for third party libraries; but although I have created a System.ServiceModel.Contracts.dll and am pointing my project to it, it doesn't seem to be having an effect. Is there a way to debug these kinds of issues?

---

Moderator | MCTS .NET 2.0 Web Applications | My Blog: http://www.commongenius.com

Answer 14

I think that:

SecurityBindingElement.CreateUserNameOverTransportBindingElement()

Should Ensure not-null. Also there are the properties .LocalClientSettings and .LocalServiceSettings.

Answer 15

Here are two:

System.Data.SqlClient.SqlCommand.Parameters.Get
add: Ensures(Result(Of SqlParameterCollection) IsNot Nothing)

System.Data.SqlClient.SqlException.Get
add: Ensures(Result (Of SqlErrorCollection) IsNot Nothing)

 

And probably more properties under System.Data that will never return Nothing

Answer 16

What about the XNA framework, or should I be asking those guys?

Answer 17

X509Certificate2Collection.Find in the System.Security.Cryptography.X509Certificates namespace.

Answer 18

Hi,
I creating a new type of Table control derived from TableLayoutPanel and I'm overriding some methods, namely OnCellPaint and OnControlAdded. These methods don't appear to have any contracts requiring that the event argument be != null.

Toby.

Answer 19

System.Windows.Forms.Control.DataBinding

Property is never Nothing and could use an ensures

Answer 20

preconditions for

System.Configuration.Provider.ProviderBase Initialize method

and

System.Configuration.SettingsProvider GetPropertyValues and SetPropertyValues methods

and

all methods on System.Web.Profile.ProfileBase, System.Web.Profile.ProfileProvider and System.Web.Security.MembershipProvider

and

the same for any other method for any other class derived from System.Configuration.Provider.ProviderBase I suppose.

please

Answer 21

Hi MaF,

Please add PureAttribute to the System.Web.Mvc.AjaxRequestExtensions.IsAjaxRequest method so that it can be used in preconditions for ASP.NET MVC controller methods that are only intended to be called by AJAX requests.

Thanks,
Dave

---

http://davesexton.com/blog

Answer 22

Are you asking about 2.0-3.5 framework types as well?  Or just 4.0?

Is there any way to crowd-source the contracts?

Answer 23

There are various things missing in the LINQ extension methods. For example, Any should Ensure `Result == Contract.Exists(source, predicate)`. This might require a change to the signature of `Contract.Exists`, since that is a `Predicate<T>` and the LINQ methods take `Func<T,bool>` instead. I figure Code Contracts are more likely to change than System.Core ;)

Answer 24

A few of us here were thinking that can't code contracts automatically report back to you guys whenever we put in an Assume on a .NET CLR type?

Yes there is a chance we will do an Assume wrongly - but this is something you can check?

Answer 25

I've spotted a few missing contracts as well:

• StackTrace and StackFrame
• MEF classes (in System.ComponentModel.Composition)
• System.Diagnostics.FileVersionInfo.GetVersionInfo (never returns null)
• Reflection methods (e.g. Assembly.GetX methods)
• System.Configuration.Install.InstallContext (Parameters property is never null)
• TPL classes (in System.Threading.Tasks), e.g. Task.Factory is never null.

What is the expected time frame from reporting missing contracts here to seeing them implemented in a future release of Code Contracts?

Answer 26

You can try using the "check assumptions" feature of the static checker.

f

 

Answer 27

We will be happy to add those contracts. Can you help us by giving more details on which classes/methods?

 

Thanks

f

Answer 28

System.Windows.Controls.Validation, PresentationFramework

There are no contracts at all.

Answer 29

Here are a couple more possible contracts to add:

MemoryCache.Default (not null)

Initializing log4net by using the class name throws a contract warning:

        private static readonly ILog _logger = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);

(CodeContracts: Possibly calling a method on a null reference 'System.Reflection.MethodBase.GetCurrentMethod()')

Answer 30

It seems MethodBase.GetCurrentMethod() can actually return null.
http://stackoverflow.com/questions/1799321/c-2-0-can-methodbase-getcurrentmethod-return-null
But I also interested in under what conditionas it will return null.

BTW, this method is very slow:
http://stackoverflow.com/questions/4885582/methodbase-getcurrentmethod-performance

Answer 31

Is there a way to express that for IDictionary<TKey, TValue> there is an implied condition that Count == Keys.Count == Values.Count ? 

---

Burt Harris

Answer 32

1. System.Environment.GetFolderPath(folder) has wrong Ensures(result.Length > 0). Actually result may be empty if folder doesn't exist

2. Please add Ensures(result != null) to System.Environment.GetFolderPath(folder, option) overload

Answer 33

TimeSpan.Zero.Milliseconds == 0

static void DoStuff(TimeSpan x)

{

Contract.Requires(x.Milliseconds == 0);

}

static void Main(string[] args)

{

DoStuff(TimeSpan.Zero);

Answer 34

Now Rect has contracts the following have popped up:

 

System.Windows.Controls.RowDefinition.ActualHeight

System.Windows.Controls.ColumnDefinition.ActualWidth

System.Windows.FrameworkElement.ActualHeight

System.Windows.FrameworkElement.ActualWidth

Answer 35

System.Data.Objects.ObjectContext

 

ObjectStateManager can not be null

public ObjectStateManager ObjectStateManager { get { if (this._cache == null) { this._cache = new ObjectStateManager(this._workspace); } return this._cache; } }

Answer 36

Is there any way for a struct to prove behaviour after a call to the implicit constructor?

ie: the assume should be able to be removed from the following code.

 

var rect = new Rect();

Contract.Assume(!rect.IsEmpty);

Answer 37

PresentationFramework

Contract.Ensures(Contract.Result != null)

on 

System.Windows.Controls.Grid.ColumnDefinitions

and

System.Windows.Controls.Grid.RowDefinitions

 

 

Answer 38

PresentationFramework

System.Windows.Data.Bindings cannot return null

 

Answer 39

System.Threading.Tasks.TaskExtensions.Unwrap and Unwrap<T> should require and ensure non-null.

Answer 40

Please mark both overloads of System.Runtime.InteropServices.Marshal.SizeOf as [Pure] and add Ensures(result > 0) to them.

And Marshal.SizeOf(Type t) should have Requires(t != null)

And Marshal.SizeOf(object structure) should have Requires(structure != null)

Answer 41

That should be result >= 0. The size can be 0 for structs with no actual members.

Answer 42

Alex, it cannot be 0. Just checked in debugger:

struct X {}

Marshal.SizeOf(typeof(X)) == 1

Answer 43

Please add the following Requires to System.Windows.Window properties:

Left & Top: value >= int.MinValue && value <= int.MaxValue || double.IsNaN(value)

Width & Height: value >= 0 && value <= int.MaxValue || double.IsNaN(value)

Answer 44

The contracts for System.Windows.Rect are incomplete - all properties can be NaN.

Requies for Width/Height setters should look like this:

 !this.IsEmpty
 value >= 0 || double.IsNaN(value)
 //OR: !(value < 0) -- shorter, but not sure if the static checker will properly handle this

Ensures for Width/Height getters should be:

 this.IsEmpty || result >= 0 || double.IsNaN(value)
 //OR: this.IsEmpty || !(result < 0)

Ensures for X/Y/Width/Height setters should be:

 this.X == value || double.IsNaN(value) && double.IsNaN(this.X)
 //OR: !(this.X != value)
 //OR: this.X.Equals(value)

Contracts for System.Windows.Size have similar problem

Answer 45

More missing contracts for System.Windows.Rect:

1. no contracts at all for Left/Top properties -- these are readonly accessors to X and Y and should ensure that Left == X and Top == Y

2. X property ensures that when a Rect is empty then X is +Infinity; Width property should ensure that when a Rect is empty then Width is -Infinity (same for Height)

 

Answer 46

TimeSpan.Zero is a readonly field to which we cannot attach a contract yet :-(

f

Answer 47

i've added a contract. However please note that it returns != null if and only if the parameter is not null

 

f

Answer 48

Please add to System.Windows.Application.LoadComponent(Uri resourceLocator):

Requires(resourceLocator != null);

Ensures(result != null);

Answer 49

Hi Alexey,

  I've added it (i've deleted the previous post to mark this fact)

 

thanks

f

Answer 50

System.Data.Sql.SqlDataSourceEnumerator.Instance

cannot return null

Neither can 

System.Data.Sql.SqlDataSourceEnumerator.GetDataSources

Answer 51

Hi Francecso,

I thought it was some forum failure (the post disappeared so quickly). Since you added the contract for List<T>.Capacity, I delete the post.

Thank you.

Answer 52

Random.NextDouble() already has: Ensures result >= 0.0

But it is missing: Ensures result < 1.0

NOTE: It's < 1.0, not <= 1.0

 

Answer 53

IAsyncResult.AsyncWaitHandle != null

---

Moderator | MCTS .NET 2.0 Web Applications | My Blog: http://www.commongenius.com

Answer 54

The FileStream constructor should have something like:

 

Contract.Ensures(CanRead == access.HasFlag(FileAccess.Read));
Contract.Ensures(CanWrite == access.HasFlag(FileAccess.Write));

Answer 55

Enum.HasFlag needs this for the static checker to be able to verify usages:

Contract.Ensures(Contract.Result<bool>() == ((this & flag) == flag));

 

Answer 56

BlockingCollection<T> in its entirety too please.

Answer 57

TaskCompletionSource and Task are missing contracts. Biggest offenders are the TaskCompletionSource.Task member not being marked non-null, and Task.ContinueWith not ensuring non-null results.

Answer 58

System.Windows.Controls.ListBox.SelectedItems

Please add Ensures(result != null)

Answer 59

System.Windows.Interop.WindowInteropHelper

constructor public WindowInteropHelper(Window window)
should have Contract.Requires(window != null) 

Answer 60

Shouldn't Collection<T>.Add()'s contract be: ensures this.Count = old(this.Count) + 1? Rather than ensures this.Count >= old(this.Count).

Regards,
Alex

Answer 61

this.Count = old(this.Count) + 1 would be more restrictive then this.Count >= old(this.Count). 

The current contract allows to create collections in which more then 1 item is added or even nothing when the Add method is called. There could be use cases for derived collection classes that duplicate items are ignored or use cases that more items are automatically added for some domain specific design rule. 

Answer 62

System.Environment.OSVersion needs an ensures(result != null) contract.

Answer 63

System.IntPtr.Size needs some sort of contract. According to documentation, it can be 4 or 8 depending on platform bitness.

Answer 64

System.Linq.Expressions.Expressions.AddAssign needs an Ensure(result != null) Contract.

Answer 65

Please add the following postconditions to the following System.Text.StringBuilder constructors:

    ensures result.Length == (value == null ? 0 : value.Length) to StringBuilder(string value);

    ensures result.Length == (value == null ? 0 : value.Length) to StringBuilder(string value, int capacity)

    ensures result.Length == length to StringBuilder(string value, int startIndex, int length, int capacity)

The last one needs the following preconditions as well:

    requires startIndex >= 0

    requires length <= (value == null ? 0 : value.Length) - startIndex

 

Answer 66

No, it's perfectly valid for it to return null.

Answer 67

XmlNode.set_InnerText should require value != null

XmlNode.set_InnerXml should require value != null

XmlNode.set_OuterXml should require value != null

 

Answer 68

If you violate this one, it's AccessViolationExceptions and ExecutionEngineExceptions all over town. :)

Any character in a string cannot be NUL ('\0') or a large number of methods in the framework fail or do bad things to the stack.

Answer 69

System.Web.HttpResponseBase.Cookies != null

System.Web.HttpRequestBase.Cookies != null

System.Net.WebRequest.Create(...) != null

 

Some MVC stuff (seems like MVC team has no contract assemblies at all):

System.Web.Mvc.GlobalFilters.Filters != null

System.Web.Mvc.ControllerBase.ViewData != null

Answer 70

AsyncOperationManager.CreateOperation(...) should ensures that the result is != null

Answer 71

Sorry if this is the wrong thread, but I've noticed a small bug in an existing contract.

In mscorlib.Contracts.dll:

The System.Collections.DictionaryEntry contracts require the value of the Key property to be non-null (in the setter as well as the constructor).  The documentation (http://msdn.microsoft.com/en-us/library/system.collections.dictionaryentry.dictionaryentry.aspx) specifies that the non-null requirement was lifted with .NET 2.0.

Answer 72

1. Contract.Ensures(Contract.Result<ICryptoTransform>() != null) for set of methods SymmetricAlgorithm.CreateDecryptor / SymmetricAlgorithm.CreateEncryptor

2. VirtualPathData.VirtualPath != null

3. RouteTable.Routes != null

4. ResourceSet.GetEnumerator() != null

Answer 73

Hi MaF,

Please add non-null return value postconditions for all properties on these classes, if possible:

• System.Windows.Input.ApplicationCommands
• System.Windows.Input.ComponentCommands
• System.Windows.Input.MediaCommands
• System.Windows.Input.NavigationCommands
• System.Windows.Documents.EditingCommands

Thanks,
Dave

---

http://davesexton.com/blog

Answer 74

HttpApplication.Server != null

Answer 75

This doesn't work for ISet<T>.

Answer 76

Several contracts for char.ConvertFromUtf32:

 

Contract.Ensures(Contract.Result<string>() != null);
Contract.Ensures(Contract.Result<string>().Length >= 1);
Contract.Ensures(Contract.Result<string>().Length <= 2);

Answer 77

1. System.Type.GetGenericTypeDefinition() != null

Answer 78

System.Delegate.CreateDelegate() != null when throwOnBindFailure == true

Answer 79

System.Linq.Enumerable.OfType<TResult>():

Contract.Ensures(Contract.ForAll(Contract.Result<IEnumerable<TResult>>(), _ => _ != null));

 

Answer 80

HttpWebRequest.GetRequestStream

SqlConnection.CreateCommand

SqlCommand.Parameters

SqlCommand.ExecuteReader

ConcurrentBag.ToArray

 

can you have Pex generate all these for you?

Answer 81

System.Data.DataRow.Table != null

Answer 82

ParallelQuery<>.ToArray<>()

And probably a bunch of other PLinq methods.

Answer 83

 

System.ServiceModel.Channels.Message.Headers != null

System.ServiceModel.Channels.Message.CreateBufferedCopy() != null

System.ServiceModel.Dispatcher.IClientMessageInspector contracts

System.ServiceModel.Channels.MessageHeader contracts

System.ServiceModel.Description.IEndpointBehavior contracts

System.ServiceModel.Dispatcher.ClientRuntime.MessageInspectors != null

System.Net.HttpWebResponse.GetResponseStream() != null (not sure)

System.ServiceModel.OperationContext.Extensions != null

System.ServiceModel.Dispatcher.ChannelDispatcher.Endpoints != null
System.ServiceModel.Dispatcher.EndpointDispatcher.DispatchRuntime != null
System.ServiceModel.Dispatcher.DispatchRuntime.MessageInspectors != null
 Guid.ToString()  : Ensures(!string.IsNullOrWhiteSpace(result))

Answer 84

There really should be an easy way to add contracts to existing libraries.

Instead of only executable contracts (DLLs) why not add the possibility to have just the metadata? Say an XML file with the contracts. This could be easily editable and upgradable.

---

Paulo Morgado

Answer 85

TaskScheduler.Current != null

SaveFileDialog.InitialDirectory != null (get/set)

DrawingVisual.RenderOpen() != null

Answer 86

System.Web.UI.WebControls.TextBox:

Text != null

Text.Length <= MaxLength

 

Answer 87

there has to be a better way than this. how long has it been now since all these requests have been posted, and we haven't had an update?

it's really a shame that you guys did all the hard work of writing the tool, but forgot the essential part of making it work effectively on anything more than the simplest test cases.

Answer 88

We don't expect acknowledgement to these. They are simply a request for contracts in a particular area. These DO get added, just not responded to in this forum.

Answer 89

System.Windows.Controls.ItemsControl:

Items != null

ItemContainerGenerator != null

System.Windows.Controls.TextBox:

Text != null (getter only - this may be set to null, but will just be coerced back to string.Empty)

SelectionStart >= 0

SelectionLen >= 0

SelectionStart + SelectionLen <= Text.Length

MaxLength >= 0

System.Windows.UIElement:

 OnPreviewLostKeyboardfocus(KeyboardFocusChangedEventArgs e), e!= null

 OnPreviewKeyDown(KeyEventArgs e), e != null

Answer 90

This is what the contract reference DLLs are for, but there's no way to create one from scratch for another DLL at the moment... I guess you *could* craft one by hand :)

Answer 91

I *think* these are correct:

Delegate.Method does not return null

MethodInfo.GetMethodBody does not return null

MethodBody.GetILAsByteArray does not return null

Answer 92

Assembly.LoadFrom(...) != null

Answer 93

sorry for no formatting, jquery script hangs in both FF and IE on that page for me ResourceSet.GetEnumerator() != null System.Web.HttpResponseBase.Cookies != null System.TimeZone.CurrentTimeZone != null System.Web.Routing.RouteTable.Routes != null System.Security.Cryptography.SymmetricAlgorithm.CreateEncryptor() != null System.Security.Cryptography.SymmetricAlgorithm.CreateDecryptor() != null System.Globalization.CultureInfo.Parent != null System.Net.WebRequest.Create(...) != null System.ServiceModel.Channels.MessageBuffer.CreateMessage() != null System.ServiceModel.Dispatcher.EndpointDispatcher.DispatchRuntime != null !string.IsNullOrWhiteSpace(Guid.ToString()) !string.IsNullOrEmpty(System.Reflection.AssemblName.Name) System.Web.HttpRequestBase.Params != null System.Web.HttpRequestBase.QueryString != null System.Globalization.CultureInfo.GetCultures() != null

Answer 94

Some more:

TypeDescriptor.GetConverter() != null

DirectoryInfo.GetDirectories() != null

DirectoryInfo.GetDirectories() Ensures: ForAll(Result, x => x != null)

DirectoryInfo.GetFiles() Ensures: ForAll(Result, x => x != null)

ICustomFormatter.Format() Requires: (format != null)

Answer 95

We can't expect that every consumer creates the contracts assembly. There must be a way to create contracts from the consumer side. Probably the team should focus on this first. -- Paulo Morgado http://www.PauloMorgado.NET/

---

Paulo Morgado

Answer 96

System.Linq.IQueryProvider, System.Core
CreateQuery(Expression) Requires: (expression != null)
Execute<TResult>(Expression) Requires: (expression != null)
Execute(Expression) Requires: (expression != null)

---

Brice Lambson

Answer 97

System.Xml.XmlNode.OwnerDocument != null System.Xml.XmlAttributeCollection.Append() != null

Answer 98

RegistryKey.GetValue(string, object) != null if object != null

Answer 99

System.Web.Routing.RouteData.Values != null

Answer 100

System.Globalization.CultureInfo.CurrentUICulture.DateTimeFormat != null

Answer 101

The whole of ArraySegment

Answer 102

System.ServiceModel.ServiceHostBase.ChannelDispatchers != null

System.AppDomain.CurrentDomain.BaseDirectory.Length < 260

System.Xml.XmlAttributeCollection.Append() != null

Answer 103

IPEndPoint, e.g. to Ensure() that Port is in the allowable range.

Answer 104

System.Web.Script.Serialization.JavaScriptSerializer.Serialize(..) != null

Answer 105

System.Linq.Enumerable.First()/Last() has: Contract.Requires(source.Count<TSource>() > 0, null, "Count(source) > 0"); propose: Contract.Requires(source.Any() || source.Count<TSource>() > 0, null);

Answer 106

Directory.Exists has this precondition:

Contract.Requires((bool) (path != null), null, "path != null");

This precondition is not needed, because Exists() returns false when path is null or empty (the same way File.Exists does, which has no precondition!)

Answer 107

*removed some invalid contracts*

I think IDictionary should require key != null in several methods (this[], get, add, ...).

Answer 108

I believe MemberInfo.DeclaringType can be null for global methods (not supported in C# but can still happen) or DynamicMethods.

Nullable.GetUnderlyingType() returns null if the passed in type is not a Nullable<> type.

I seem to remember dictionaries support null keys as long as the equality comparer used also supports them.

Answer 109

Oops. I should have checked these beforehand... the reflection API seems to be at odds with the rest of the standard library, returning NULL when the argument is invalid.

WRT dictionaries, the standard Dictionary class doesn't support null keys at all, even if the equality you've set does.

Answer 110

DateTimeOffset.Year > 0
DateTimeOffset.Year <= 9999
DateTimeOffset.Month > 0
DateTimeOffset.Month <= 12
DateTimeOffset.Day > 0
DateTimeOffset.Day <= 31
DateTimeOffset.Hour >= 0
DateTimeOffset.Hour < 24
DateTimeOffset.Minute >= 0
DateTimeOffset.Minute < 60
DateTimeOffset.Second >= 0
DateTimeOffset.Second < 60
DateTimeOffset.Millisecond >= 0
DateTimeOffset.Millisecond < 1000

Answer 111

DateTime.Millisecond >= 0
DateTime.Millisecond < 1000

Answer 112

System.Diagnostics.Stopwatch.StartNew() != null

Answer 113

System.Linq.Expressions.Expression<>.Compile() != null

Answer 114

System.Xml.XmlNode.OuterXml != null

Answer 115

DateTime.get_Ticks() should ensure that the result is at most 3155378975999999999, not 3155378976000000000.

Answer 116

ICustomFormatter.Format should require format != null

Answer 117

System.Globalization.RegionInfo.DisplayName != null

System.ComponentModel.Composition.Hosting.AggregateCatalog.Catalogs != null

System.Reflection.AssemblyName.Version != null

System.Reflection.AssemblyName.Name != null

or better yet...

!string.IsNullOrWhiteSpace(System.Reflection.AssemblyName.Name)

Answer 118

System.Windows.Media.FormattedText:
Width >= 0
Height >= 0

System.Windows.Thickness:
Left >= 0
Right >= 0
Top >= 0
Bottom >= 0

System.Array:
ConvertAll<,>(,) != null