Index for FK create with "WHERE IS NOT NULL" condition by default

[pbhofstede2]

From firebird-support group: https://groups.google.com/g/firebird-support/c/xNOqT9-88MQ

FB 5.0.3 (as well on earlier 5.x versions).
I've got a query like

select
t1.ID
from tableX t1
where
(t1.FK2 IS NULL) and
(t1.FK1 = char_to_uuid('9A05D014-1414-4B93-ADC3-1723C47F80E9')) and
(t1.INTFIELD = 2) and
(t1.DATEFIELD = '19.10.2024')

PLAN is:
PLAN (T1 INDEX (COMPOUND_IDX4, FK2_IDX))

COMPOUND_IDX4 = (FK1, INTFIELD, DATEFIELD);
FK2_IDX = (FK2)

SQL Duration: 1s734ms
Fetches from cache = 23.754

When I force to don't use the index of the FK2-field using coalesce (its char(16) OCTETS):

select
t1.ID
from tableX t1
where
(coalesce(t1.FK2, NULL) IS NULL) and
(t1.FK1 = char_to_uuid('9A05D014-1414-4B93-ADC3-1723C47F80E9')) and
(t1.INTFIELD = 2) and
(t1.DATEFIELD = '19.10.2024')

PLAN Is:
PLAN (T1 INDEX ( COMPOUND_IDX4 ))

SQL Duration: 0s015ms
Fetches from cache = 843

Recordcount result = 839
selectivity COMPOUND_IDX4 = 0,000001068938
selectivity FK2_IDX = 0,000003139274

Suggestion:
Let foreign keys be able to use partial indexes and by default apply "WHERE IS NOT NULL" condition.
Related to:
#7964, #7258
Make FOREIGN KEY constraint to use any suitable index