TeeChart: Nullvalues & Automatic scaling of axes

Hey Experts

When a record in my dataset has an empty field, the add-null value feature
spoils the automatic scaling of axes, as the null-field is considered as 0.
For example, I have a series which numbers between 80 and 120, but if I have
an empty field, the min-value on the axis is set to 0.
Doe anyone know how to avoid this? it is a rel pain in the ....