Since 87456218dcc9, record with NULL field is include in nested negative clause
but this should not applied if the operand is or contains None.
Closes#13911
(grafted from 993d890dd786424c2cd00009045ad95a09075e72)
--HG--
branch : 6.0
This unify the search behavior on relational fields with NULL value started
with c14f51b77b30.
Closes#13585
(grafted from 87456218dcc9b075658f9e2338b120fce9b9a43d)
--HG--
branch : 6.0