Marcelo,
Once an object is released the memvar that pointed to it will have a .NULL. value and still be type "O". I'm not sure what you mean by "can I change this .null."
ox = createobject( "form" )
ox.Visible = .t.
? type( "ox" ) && now it's O
ox = 123 && releases the form and changes the memvar to a numeric
? type( "ox" )
>If you have a Form or another object that is not created with CREATEOBJECT, it takes .NULL. value.Ok? Well, can I change this .NULL. value by "O" value with TYPE() or any other command ?