What's wrong with my SQL trigger with ORA-00900?

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Oracle

trigger

What's wrong with my sql?I want to write a trigger to insert the increment id before insert the row.It show that the trigger state is invalid.

create or replace trigger MYDB.tri_t_form_382
before insert on MYDB.t_form_382 referencing new as new_value 
for each row  
begin 
    if :new_value.id is null or  :new_value.id=0 then
        select MYDB.seq_t_form_382.nextval into :new_value.id from dual; 
    end if;
end tri_t_form_382;

And it shows:

Navicat:

[Err] ORA-24344: success with compilation error
DB SOLO 5:

09:34:04> end if

[Err] ORA-00900: invalid SQL statement
How to fix it?

What I have tried:

I have try to delete the end if string,but it is still wrong.