SQL & PL/SQL :: Create A Row-level Trigger Named TRG_PROB_FEE?

I'm trying to create a row-level trigger named TRG_PROB_FEE to run before insert or update of the problem fee attribute on the problem table. If the associated DML command would result in a null for the problem fee(prob_fee), then get the value of the problem fee attribute from the associated contract (con_probfee) to use as the value for problem fee (prob_fee) in the Problem table.

CREATE OR REPLACE TRIGGER TRG_PROB_FEE
BEFORE INSERT OR UPDATE OF PROB_FEE ON PROBLEM
FOR EACH ROW
BEGIN
IF :NEW.PROB_FEE IS NULL THEN
SELECT CON_PROBFEE
INTO PROBLEM
FROM CONTRACT
WHERE CON_PROBFEE = :NEW.PROB_FEE
END IF;
END;
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