If you use the Sharepoint Create Item action and the source is a null Lookup field (either from the trigger or a GetItem) then the create will fail because setting a lookup field to Null throws an error.   Since many times lookup fields are not selected and are indeed empty (null) this becomes a complex issue to handle particularly when using FLOW to archive (or copy) items from one list to another.   This is really a Software Design 101 problem that has existed for a long time in Sharepoint Designer -- its really easy to fix check for null before trying to set a Lookup Field and do nothing if its null.   Working around this in Flow is absurdly difficult -- probably could do it with condition claues but what if you have 4 lookup columns any combidnation could be null -- just imagine the complexity of the condiition actions and Create Action to cover all the permutations of possibilities with 4 lookups.     ... View more