question on multi-valued forms widget

Hi there,

In the documentation it says:
Before Cocoon 2.1.8, multivaluefields required a selection list, since 
no input method was available for multivaluefields without a selection 
list. Since Cocoon 2.1.8, this requirement has been dropped and a 
free-entry multivaluefield styling is available.

My question is what should the free-entry multivaluedfield  look like?  
I tried this, in Cocoon 2.1.11:

<fd:multivaluefield id="Icecream">
<fd:datatype base="string"/>
<fd:selection-list>
<fd:item value="vanilla"/>
<fd:item value="straberry"/>
<fd:item value="peach"/>
<fd:item value="chocolate"/>
</fd:selection-list>
</fd:multivaluefield>

  but get a NPE on setValues() as in java.lang.NullPointerException at 
org.apache.cocoon.forms.formmodel.MultiValueField.setValues(MultiValueField.java:225)

Paul