Need help on plsql varray

Hi Team ,

iam running the below program on oracle varray . I need to print the current element , previous element in the dbms_output statement. But i get the below error  when i run the program

Error starting at line 2 in command:
declare
type v_numvarr  is varray(10) of number;
l_numvarr v_numvarr;
cnt simple_integer:=1;
begin

l_numvarr :=v_numvarr();
l_numvarr.extend;
l_numvarr(1):=10;
l_numvarr.extend;
l_numvarr(2):=20;
l_numvarr.extend(8);
l_numvarr(3):=30;
l_numvarr(4):=40;
l_numvarr(5):=50;
l_numvarr(6):=60;
l_numvarr(7):=70;
l_numvarr(8):=80;
l_numvarr(9):=90;
l_numvarr(10):=100;
-- l_numvarr(11):=110 this will cause an error , because we are accessing invalid index  position , the maximum numbe is 10 , we are accessing 11
dbms_output.put_line ('The total size of the array is: '||l_numvarr.limit);

/*
for i in l_numvarr.first..l_numvarr.last
loop
dbms_output.put_line ('The element at index position ('||i||') is:' || l_numvarr(i));
end loop;
*/

l_numvarr.trim;

for i in l_numvarr.first..l_numvarr.last
loop

dbms_output.put_line ('The element at index position ('||i||') is:' || l_numvarr(i) ||l_numvarr(l_numvarr(l_numvarr.prior(i))) );

end loop;

/*
l_numvarr.trim(2);


for i in l_numvarr.first..l_numvarr.last
loop

dbms_output.put_line ('The element at index position ('||i||') is:' || l_numvarr(i));

end loop;*/
end;
Error report:
ORA-06502: PL/SQL: numeric or value error: NULL index table key value
ORA-06512: at line 36
06502. 00000 -  "PL/SQL: numeric or value error%s"
*Cause:    
*Action:





--- Program


declare
type v_numvarr  is varray(10) of number;
l_numvarr v_numvarr;
cnt simple_integer:=1;
begin

l_numvarr :=v_numvarr();
l_numvarr.extend;
l_numvarr(1):=10;
l_numvarr.extend;
l_numvarr(2):=20;
l_numvarr.extend(8);
l_numvarr(3):=30;
l_numvarr(4):=40;
l_numvarr(5):=50;
l_numvarr(6):=60;
l_numvarr(7):=70;
l_numvarr(8):=80;
l_numvarr(9):=90;
l_numvarr(10):=100;
-- l_numvarr(11):=110 this will cause an error , because we are accessing invalid index  position , the maximum numbe is 10 , we are accessing 11
dbms_output.put_line ('The total size of the array is: '||l_numvarr.limit);

/*
for i in l_numvarr.first..l_numvarr.last
loop
dbms_output.put_line ('The element at index position ('||i||') is:' || l_numvarr(i));
end loop;
*/

l_numvarr.trim;

for i in l_numvarr.first..l_numvarr.last
loop

dbms_output.put_line ('The element at index position ('||i||') is:' || l_numvarr(i) ||  ' Previous element :'||   l_numvarr(l_numvarr(l_numvarr.prior(i))) );

end loop;

/*
l_numvarr.trim(2);


for i in l_numvarr.first..l_numvarr.last
loop

dbms_output.put_line ('The element at index position ('||i||') is:' || l_numvarr(i));

end loop;*/
end;
/