IN PLSQL TO CHECK IF a VALUE IS NOT NULL, you must USE the "IS NOT NULL" syntax.
 
FOR example,
 
IF Lvalue IS NOT NULL THEN
 
    ...
 
END IF;
 
IF Lvalue does NOT contain a NULL VALUE, the "IF" expression will evaluate TO TRUE.
 
 
 
You can also USE "IS NOT NULL" IN an SQL statement. FOR example:
 
SELECT * FROM suppliers
WHERE supplier_name IS NOT NULL;
 
This will RETURN ALL records FROM the suppliers TABLE WHERE the supplier_name does NOT contain a NULL VALUE.