Attribute 'ref' is not allowed to appear in element 'camel:unmarshal'

[Tim de Wit]

I'm trying to upgrade camel from 2.15.2 to 3.2.0 and I keep getting the 
following error:

Caused by: org.xml.sax.SAXParseException; lineNumber: 262; columnNumber: 39; 
cvc-complex-type.3.2.2: Attribute 'ref' is not allowed to appear in element 
'camel:unmarshal'

My camel context.xml contains:

        <camel:dataFormats>
            <camel:hl7 id="hl7Format" validate="false"/>
        </camel:dataFormats>

        <camel:route id="routeHL7in">
            <camel:from uri="ref:endpointHl7In"/>
                        <camel:transacted/>
                        <camel:unmarshal ref="hl7Format" />
                        <camel:choice>
                <camel:when>
                        ...

The other "ref=" were replaced by "uri=ref:" but for (un)mashal that doesn't 
seem to work. Ideas anyone?

regards, Tim