Note that the parentheses are not considered part of the input-argument list, so a request-message-label without an input-argument-list may still optionally include an empty set of parentheses (“()”) after the message-name. Source Unified Modeling Language 2.5.1
If a request-message-label does not include an input-argument-list and the Message has a signature, then this denotes that the Message has wildcard arguments corresponding to all in and inout ownedParameters of an Operation or attributes of a Signal ... Source Unified Modeling Language 2.5.1
