Null values / Numeric fields / DataControl

On a form, put :
A DataControl
A TextBox (or any other edit Control, bound to a numeric field of the database that the DataControl manages(The REQUIRED property of the field is well set to FALSE)
The TextBox correctly read data from the numeric field and correctly write data looking like numeric values ... OK BUT ...
When setting the TextBox to blank (= erasing previously recorded data), and trying to update the database with the new "NULL" value : CRASH (message : "data conversion error")
Nevertheless, if you perform this update programmatically, it works :
MyRecordset.edit
MyRecordset.MyField = Null MyRecordset.update

I think it's because of the dataControl itself ... How to make it able to accept Null strings as Null values for numeric fields ???

Thank you for your help.

Is that a DAO data control or ADO data control?