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

Abre xml/System.ServiceModel.Channels/MessageProperties.xml y localiza la documentación de MessageProperties.Item[string]. Compara el comportamiento indicado con la implementación vinculada de MessageProperties.cs. Actualiza la documentación para describir el comportamiento cuando la propiedad no existe y, después, verifica que el texto renderizado del valor devuelto coincida con la implementación.

Escrito por el modelo de indexación a partir del texto del issue.