issue a warning when get_slivers is used against an existing but empty slice e.g. with this code one gets an exception when trying to renew an existing slice that has no node the warning would help spotting this
issue a warning when get_slivers is used against an existing but empty slice
e.g. with this code one gets an exception when trying to renew an existing slice that has no node
the warning would help spotting this

onelab-eu/sfa,onelab-eu/sfa,yippeecw/sfa,onelab-eu/sfa,yippeecw/sfa,yippeecw/sfa