Access 2003 conditional formatting and field with NULL value not return NULL

Question

The field is taken from the table and is the source of data for the textbox, in which I want to apply conditional formatting. Almost always it is NULL . The expression for the conditional formatting:

Not IsNull ([duedate])

Always returns true, I do not understand why. Field [duedate] belongs to the parent form.

Answer 1

我认为您还需要像IsNull一样检查长度

Len(Field) = 0