[FIX] base_external_referential: importing an empty field of type list give an empty list to mapping functions so we do not have to care in the mappings functions if ifield is a list or not, it should always be a list. 
[FIX] base_external_referential: importing an empty field of type list give an empty list to mapping functions so we do not have to care in the mappings functions if ifield is a list or not, it should always be a list. 

hugosantosred/connector,mohamedhagag/connector,Endika/connector,brain-tec/connector,BT-jmichaud/connector,esousy/connector,js-landoo/connector,Antiun/connector,acsone/connector,zhaohuaw/connector,anybox/connector,sylvain-garancher/connector,guewen/connector,open-synergy/connector,anybox/connector,brain-tec/connector,dvitme/connector,MindAndGo/connector,zhaohuaw/connector,js-landoo/connector,sylvain-garancher/connector,guewen/connector,fevxie/connector,Antiun/connector,BT-fgarbely/connector,gurneyalex/connector,BT-ojossen/connector,mohamedhagag/connector,hugosantosred/connector,gurneyalex/connector,open-synergy/connector,dvitme/connector,esousy/connector,BT-fgarbely/connector,MindAndGo/connector,BT-jmichaud/connector,acsone/connector,maljac/connector,fevxie/connector,acsone/connector,brain-tec/connector,BT-ojossen/connector,maljac/connector,Endika/connector