Heat stack update fails when multi-attach volume present

I am trying to deploy a Murano application that creates a multi-attach volume. My Openstack deployment is based on Queens where multi-attach is supported.

This is the Heat error I get when I deploy my application.

Multiattach volumes are only supported starting with compute API version
2.60. (HTTP 400) (Request-ID: req-9d0d889d-03a6-4a90-8007-233de8717804)

After making sure that Heat was using python-novaclient version 10.0 instead of 9.1,
I found the problem lies in this file:

heat/engine/resources/openstack/nova/server.py as follows:

 def handle_create(self):
    .
    .
    .
     try:
            api_version = None
            # if 'auto' or 'none' is specified, we get the string type
            # nics after self._build_nics(), and the string network
            # is supported since nova microversion 2.37
            if isinstance(nics, six.string_types):
                api_version = self.client_plugin().V2_37

            if self._is_nic_tagged(self.properties[self.NETWORKS]):
                api_version = self.client_plugin().V2_42

            nc = self.client(version=api_version)

When debugging this, I noticed that the api_version set in the Client is None. My understanding is that None means the minimum version supported. Unfortunately the minimum version is not 2.60. This explains the reason for the failure.

My temporary work-around is to change this line:

api_version = None

to

api_version = self.client_plugin().V2_60 (where V2_60 is now defined in heat/engine/clients/os/nova.py)

If you need more info or have questions, please let me know. I hope this can be solved soon.