Oracle initialization of collection elements with not null constraint - oracle

Question

What is the initialization value for NOT NULL element in the collection (Table/Varray)? It seems like the NULL but it is NOT NULL. Tested in Oracle LIVE SQL (Oracle Database 19c Enterprise Edition - 19.2.0.0.0)
declare
type TArrNotNull IS table of number NOT NULL;
type TArrAllowNull IS table of number;
arrNotNull TArrNotNull := TArrNotNull();
arrAllowNull TArrAllowNull := TArrAllowNull();
begin
-- NOT NULL ARRAY ELEMENTS
DBMS_OUTPUT.PUT_LINE('======== table/Array of number NOT NULL example ==========');
arrNotNull.Extend;
IF arrNotNull(1) is null then
DBMS_OUTPUT.PUT_LINE('NULL !!!');
else
DBMS_OUTPUT.PUT_LINE('NOT NULL BUT WHAT ???->['||COALESCE(arrNotNull(1),100)||']');
DBMS_OUTPUT.PUT_LINE('NOT NULL BUT WHAT + 1 BECOMES NULL (LIKE REAL NULL)???->['||COALESCE(arrNotNull(1)+1,100)||']');
end if ;
DBMS_OUTPUT.PUT_LINE('======== table/Array of number example ==========');
-- NOT NULL ARRAY ELEMENTS
arrAllowNull.Extend;
IF arrAllowNull(1) is null then
DBMS_OUTPUT.PUT_LINE('OK IS NULL !!!');
else
DBMS_OUTPUT.PUT_LINE('NOT NULL !!!');
end if ;
end;
RESULTS:
Statement processed.
======== table/Array of number NOT NUMBER example ==========
NOT NULL BUT WHAT ???->[]
NOT NULL BUT WHAT + 1 BECOMES NULL (LIKE REAL NULL)???->[100]
======== table/Array of number example ==========
OK IS NULL !!!
UPD: Also the same if you assign the value to the NUMBER variable.
tst:=arrNotNull(1);
if tst is null then
DBMS_OUTPUT.PUT_LINE('N NULL !!!');
else
DBMS_OUTPUT.PUT_LINE('N NOT NULL !!!+++');
end if;
if (tst+1) is null then
DBMS_OUTPUT.PUT_LINE('N+1 NULL !!!+++');
else
DBMS_OUTPUT.PUT_LINE('N+1 NOT NULL !!!+++');
end if;
RESULT:
N NOT NULL !!!+++
N+1 NULL !!!+++

Answer 1

Very interesting. Didn't find a "value" for 18+, but in 12c you get a NULL.
I did shrink your code a little:
declare
type TArrNotNull IS table of varchar2(100) NOT NULL;
arrNotNull TArrNotNull := TArrNotNull(1, 2, 3);
begin
begin
arrNotNull(2) := to_number(NULL); -- will throw, because null is not allowed
dbms_output.put_line('arrNotNull(2) is null now');
exception
WHEN others THEN
dbms_output.put_line('arrNotNull(2) couldn''t be set to null');
end;
arrNotNull.Extend;
dbms_output.put_line('arrNotNull(4): >>>' || nvl(arrNotNull(4), 'NULL') || '<<<');
end;
Result in 12c:
arrNotNull(2) couldn't be set to null
arrNotNull(4): >>>NULL<<<
Result in 18c (same like yours):
arrNotNull(2) couldn't be set to null
arrNotNull(4): >>><<<
Also interesting is, that an Extend on a nullable Table of has NULL as default value:
declare
type TArrNotNull IS table of varchar2(100);
arrNotNull TArrNotNull := TArrNotNull(1, 2, 3);
begin
arrNotNull.Extend;
dbms_output.put_line('arrNotNull(4): >>>' || nvl(arrNotNull(4), 'NULL') || '<<<');
end;
Result on all versions:
arrNotNull(4): >>>NULL<<<