Assign option datasource value using picklist

[sedmands]

I have a ComboBox populated by an OptionDataSource. Upon selecting an item from the list, I would like to assign other values associated with the selected item from the datasource to other fields within the form.

I have a changeHandler set up and am using:
form.setValue("vendorName", comboBox.getSelectedRecord().getAttribute("vendorName")); to assign the appropriate value from the optionDataSource to the dynamicForm.

When I do this, I am getting an exception with the message:

16:58:07.926 [ERROR] [manager] 16:58:07.924:WARN:PickListMenu:isc_PickListMenu_0:fields and completeFields are null and there is no DataSource

Any help would be appreciated.