MessageProperties.Item[string] can throw, but documentation claims null is returned

In the documentation for `MessageProperties.Item[string]`, it is claimed that:

> The property with the specified name, or null if the property does not exist.

This is incorrect. The code will throw an exception if the property does not exist. This is not mentioned in the documentation.

Rendered documentation:
https://learn.microsoft.com/en-us/dotnet/api/system.servicemodel.channels.messageproperties.item?view=dotnet-plat-ext-6.0&viewFallbackFrom=net-6.0#system-servicemodel-channels-messageproperties-item(system-string)

Documentation source:
https://github.com/dotnet/dotnet-api-docs/blob/main/xml/System.ServiceModel.Channels/MessageProperties.xml

dotnet/wcf source code:
https://github.com/dotnet/wcf/blob/4e2a97e639417fd14158c9e7f0bb36de342a667d/src/System.Private.ServiceModel/src/System/ServiceModel/Channels/MessageProperties.cs#L73

4.8 reference source has the same behaviour:
https://referencesource.microsoft.com/#System.ServiceModel/System/ServiceModel/Channels/MessageProperties.cs,67