SQL & PL/SQL :: Code Not Running After IF Statement?

with the code below i have created 2 varaibles v_start_date and v_finish_date, i have inputs for them, thats fine the problem is when the inputs are empty, i have put a ELSIF statement in the begin section of the code, now if the variables have input from the textbox's then it works fine but if they are empty, the programme reads into the if statement executes that bit of code but doesn't seem to open the cursor up and execute that bit of code.

DECLARE
v_start_date enrollments.enrollment_date%TYPE:= :START_DATE;
v_finish_date enrollments.enrollment_date%TYPE := :FINISH_DATE;
CURSOR no_grades_cur IS
SELECT class_id,stu_id, status
FROM enrollments

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