SELECT ROW(t.*) FROM table t and nulls with textual representation?

Hello,

is there any possibility to get null-values as text 'null' from dynamic select expression like

SELECT ROW(t.*) FROM table t

Normally you get

(t1,t2,t3,,t5,,,)

How can you get

(t1,t2,t3,null,t5,null,null,null)

I would like to use the result with dynamic update expression and update doesn't like of empty values, so

UPDATE SET (t1,t2,t3,t4,t5,t6,t7,t8) = (t1,t2,t3,,t5,,,)

generates error.

Best regards,
Teemu Juntunen, e-ngine