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: com.vaadin.data.util.converter.Converter$ConversionException: Could not convert value to String
	at com.vaadin.ui.AbstractField.convertToModel(AbstractField.java:751)
	at com.vaadin.ui.AbstractField.convertToModel(AbstractField.java:722)
	at com.vaadin.ui.AbstractField.getConvertedValue(AbstractField.java:783)
	at com.vaadin.ui.AbstractField.commit(AbstractField.java:249)
	... 39 more
Caused by: com.vaadin.data.util.converter.Converter$ConversionException: Unable to convert value of type com.vaadin.data.util.sqlcontainer.RowId to model type class java.lang.String. No converter is set and the types are not compatible.
	at com.vaadin.data.util.converter.ConverterUtil.convertToModel(ConverterUtil.java:142)
	at com.vaadin.ui.AbstractField.convertToModel(AbstractField.java:748)
	... 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.