Pass the nulls to a dynamic SQL:
Passing Nulls:
Assume that you want to pass the nulls to a dynamic SQL statement. For illustration, you may write the EXECUTE IMMEDIATE statement as shown below:
EXECUTE IMMEDIATE 'UPDATE emp SET comm = :x' USING NULL;
Though, this statement fails with a bad expression error as the literal NULL is not allowed in the USING clause. To work around this constraint, just replace the keyword NULL with an uninitialized variable, which is as shown below:
DECLARE
a_null CHAR(1); -- set to NULL automatically at run time
BEGIN
EXECUTE IMMEDIATE 'UPDATE emp SET comm = :x' USING a_null;
END;