ORACLE - regexp_substr to return null values

I have used the function regexp_substr(STR,'[^|]+',1,2), it works well at some cases but for null scenarios, it gives the third value,

1|CAT|DOG
3|HARRY|GOAT|STACK
6||LION|TIGER  --this row should return null, but the above function gives me LION

Expected Output:

CAT
HARRY
(null)