Comment 2 for bug 1381074

To follow up - I've tried it with default-network-ipam and the same thing happened :

>>> from vnc_api.vnc_api import *
>>> vnc = VncApi("admin",'contrail123',"admin","127.0.0.1","8082","/")
>>> vnc.network_ipams_list()
{u'network-ipams': [{u'href': u'http://127.0.0.1:8082/network-ipam/f9b58449-f9bc-4134-a2b1-a1a00582f404', u'fq_name': [u'default-domain', u'default-project', u'default-network-ipam'], u'uuid': u'f9b58449-f9bc-4134-a2b1-a1a00582f404'}]}
>>> ipam = vnc.network_ipam_read(id="f9b58449-f9bc-4134-a2b1-a1a00582f404")
>>> vn_blue_obj = VirtualNetwork('vn-blue')
>>> vnc.virtual_network_create(vn_blue_obj)
u'a2090cf8-a2a7-4e37-9084-485cb400287e'
>>> vn_obj = vnc.virtual_network_read(id='a2090cf8-a2a7-4e37-9084-485cb400287e')
>>> vn_obj.add_network_ipam(ipam,VnSubnetsType([IpamSubnetType(subnet = SubnetType('10.1.1.0', 24))]))
>>> vnc.virtual_network_update(vn_obj)
u'{"virtual-network": {"href": "http://127.0.0.1:8082/virtual-network/a2090cf8-a2a7-4e37-9084-485cb400287e", "uuid": "a2090cf8-a2a7-4e37-9084-485cb400287e"}}'
>>> vn_obj_upd = vnc.virtual_network_read(id='a2090cf8-a2a7-4e37-9084-485cb400287e')
>>> vn_obj_upd.del_network_ipam(ipam)
>>> vnc.virtual_network_update(vn_obj_upd)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/dist-packages/vnc_api/gen/vnc_api_client_gen.py", line 4858, in virtual_network_update
    self.ref_update('virtual-network', obj.uuid, ref_name, ref[0], list(ref[1]), 'DELETE')
  File "/usr/lib/python2.7/dist-packages/vnc_api/vnc_api.py", line 371, in ref_update
    raise he
cfgm_common.exceptions.HttpError: HTTP Status: 500 Content: Internal Server Error