Conversion Error for a ComboBox backed by SQLContainer

I have a piece of code that looks like

FieldGroup group = new FieldGroup(bean);
SQLContainer c = new SQLContainer(new TableQuery(null, "USER", "SYSTEM", pool, new OracleGenerator()));
ComboBoxoptions = new ComboBox("System", c);
group.bind(options, "system");

This is for a form.

When i try and save the form i get

Caused by:$ConversionException: Could not convert value to String
	at com.vaadin.ui.AbstractField.convertToModel(
	at com.vaadin.ui.AbstractField.convertToModel(
	at com.vaadin.ui.AbstractField.getConvertedValue(
	at com.vaadin.ui.AbstractField.commit(
	... 39 more
Caused by:$ConversionException: Unable to convert value of type to model type class java.lang.String. No converter is set and the types are not compatible.
	at com.vaadin.ui.AbstractField.convertToModel(
	... 42 more

I don’t seem to see a way of getting the correct container property, furthermore i can see a way of getting the RowId to be a String.