Subform problem

[Ling]

I have a subform which its record source is based on a
query. However, sometimes this query may not generate any
records at all.
Besides this, I have a control on the parent form that
refers to one of the controls in the subform.So, when the
subform does not have any records, this control on the
parent form shows #Error. How do I solve this? At least
make this control show a zero or null value when the
subform has no records.

Thanx

Ling