Missing SOAPAction

Hey, I have a problem I think is easy to solve but this is my 1st time researching F5 rules. I'm a developer by trade but trying to figure out an urgent issue.

I have a problem with an obscure client of our SOAP services. Our WSDLs speficy am empty SoapAction but this client assume that without a SOAPAction, it won't even send the header.

Our server get a mixture of REST and SOAP requests so I am looking for a rule that will check only SOAP requests for a SOAPAction header and if it doesn't exist, add it.

Or, is this just as easy as doing something like this? HTTP::header replace SOAPAction ""

This is a little scorched earth but we don't have any SOAPAction anywhere. I don't think this would negatively affect other types of requests even it were be added to everything?