force user to choose a registered container (but still allow empty)
force user to choose a registered container (but still allow empty)

DiamondLightSource/SynchWeb,DiamondLightSource/SynchWeb,DiamondLightSource/SynchWeb,DiamondLightSource/SynchWeb,DiamondLightSource/SynchWeb,DiamondLightSource/SynchWeb