Add the following text to the exposition on /s:Envelope/s:Body/*/wse:Filter after the second paragraph:

It is possible for a Subscribe request to contain a filter that will never evaluate to true for the lifetime of the Subscription. If an Event Source detects this condition it MAY generate a wse:EmptyFilter fault in response to the Subscribe request message.

Add the following fault definition to Section 6:

6.8 EmptyFilter

This fault MAY be generated when an Event Source detects a wse:Subscribe request containing a filter that, for whatever reason, will never evaluate to true.

[Code] s12:Sender
The wse:Filter would result in zero Notifications
The wse:Filter value.