How to Remove End Date on Responsibility using API

The removing of end date from a responsibility which is already assigned to a user, can be done using the API fnd_user_resp_groups_api

Sample Procedure for removing end date from Responsibilities given to Users:
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DECLARE

p_user_name VARCHAR2 (50) := 'XX12345';
p_resp_name VARCHAR2 (50) := 'Order Management Super User';
v_user_id NUMBER (10) := 0;
v_responsibility_id NUMBER (10) := 0;
v_application_id NUMBER (10) := 0;

BEGIN

BEGIN
SELECT user_id
INTO v_user_id
FROM fnd_user
WHERE UPPER (user_name) = UPPER (p_user_name);
EXCEPTION
WHEN NO_DATA_FOUND
THEN
DBMS_OUTPUT.put_line ('User not found');
RAISE;
WHEN OTHERS
THEN
DBMS_OUTPUT.put_line ('Error finding User.');
RAISE;
END;

BEGIN
SELECT application_id, responsibility_id
INTO v_application_id, v_responsibility_id
FROM fnd_responsibility_vl
WHERE UPPER (responsibility_name) = UPPER (p_resp_name);
EXCEPTION
WHEN NO_DATA_FOUND
THEN
DBMS_OUTPUT.put_line ('Responsibility not found.');
RAISE;
WHEN TOO_MANY_ROWS
THEN
DBMS_OUTPUT.put_line
('More than one responsibility found with this name.');
RAISE;
WHEN OTHERS
THEN
DBMS_OUTPUT.put_line ('Error finding responsibility.');
RAISE;
END;

BEGIN

DBMS_OUTPUT.put_line ('Initializing The Application');

fnd_global.apps_initialize (user_id => v_user_id,
resp_id => v_responsibility_id,
resp_appl_id => v_application_id
);

DBMS_OUTPUT.put_line
('Calling FND_USER_RESP_GROUPS_API API To Insert/Update Resp');

fnd_user_resp_groups_api.update_assignment
(user_id => v_user_id,
responsibility_id => v_responsibility_id,
responsibility_application_id => v_application_id,
security_group_id => 0,
start_date => SYSDATE,
end_date => NULL,
description => NULL
);

DBMS_OUTPUT.put_line
('The End Date has been removed from responsibility');
COMMIT;

EXCEPTION
WHEN OTHERS
THEN
DBMS_OUTPUT.put_line ('Error calling the API');
RAISE;
END;
END;