'Create a new masking view.
:param serial_number: the array serial number
:param maskingview_name: the masking view name
:param storagegroup_name: the storage group name
:param port_group_name: the port group
:param init_group_name: the initiator group
:param extra_specs: extra specifications
:returns: error_message -- string or None'

def create_masking_view(self, serial_number, maskingview_name, storagegroup_name, port_group_name, init_group_name, extra_specs):

    error_message = None
    try:
        self.rest.create_masking_view(serial_number, maskingview_name, storagegroup_name, port_group_name, init_group_name, extra_specs)
    except Exception as e:
        error_message = ('Error    creating    new    masking    view.    Exception    received:    %(e)s' % {'e': six.text_type(e)})
    return error_message
