SQL Server 2016

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create table persons (personID int);
create table documents (documentID int, personID int);

insert into persons values(10),(11),(12),(13),(14),(15);
insert into documents values (1,10),(1,11),(1,null),(2,null),(3,11),(3,15);
12 rows affected

select * from persons where personID in (12,13,14);

personID

12

13

14

select * from documents where personID in (12,13,14);

documentID
personID

select personID from documents

personID

10

11

null

null

11

15

select *
from   persons
where  personID not in (select personID from documents);

personID

select *
from   persons
where  personID not in (select personID from documents where personID is not null);

personID

12

13

14

personID
10
11
null
null
11
15