Aggregate EIP - Adds by default empty correlation expression in generated source

   <aggregate completionFromBatchConsumer="false" completionTimeout="5000" strategyRef="myStrategy">
            <correlationExpression>
                <language language="simple">${header.id}</language>
            </correlationExpression>
            <completionPredicate>
                <language language="simple"/>
            </completionPredicate>
            <completionTimeout>
                <language language="simple"/>
            </completionTimeout>
            <completionSize>
                <language language="simple"/>
            </completionSize>
            <to uri="log:done"/>
        </aggregate>