Apache nifi Nifi-PutDatabaseRecord中的空问题

在

PutDatabaseRecord

PutDatabaseRecord[id=d0bf3b91-a766-1df3-9879-a68384b28626] Failed to process 
StandardFlowFileRecord[uuid=95c2174b-8eeb-4652-a0e9-8aa5822ab8bb,claim=StandardContentClaim 
[resourceClaim=StandardResourceClaim[id=1602761141087-1040, container=default, section=16],
 offset=895492, length=636],offset=0,name=218d3ce0-96aa-4755-aaff-a4655447b61e,size=636]
 due to Batch entry 0 
INSERT INTO public.test(a, b, c, d) 
VALUES (21283, 'HILTGLOBALP-100003en_GLOBAL', 3773, NULL) ON CONFLICT (c, a) 
DO UPDATE SET (a, b, c, d) = (EXCLUDED.a, EXCLUDED.b, EXCLUDED.c, EXCLUDED.d) was aborted: ERROR: column "d" is of type integer but expression is of type character varying
      Hint: You will need to rewrite or cast the expression.
      Position: 106  Call getNextException to see other errors in the batch.

列d是FK到另一个可为空的表。请帮我解决这个问题