anchor.diff:  
   === About completion
   
  -When aggregation link:exchange.html[Exchange]s at some point you need to
  +When aggregation xref:exchange.adoc[Exchange]s at some point you need to
   indicate that the aggregated exchanges is complete, so they can be send
   out of the aggregator. Camel allows you to indicate completion in
   various ways as follows:
  
positive.code: Aggregate EIP will invoke the
  `AggregationStrategy` with `oldExchange` as null, for the first
  Exchange incoming to the aggregator. And then for
  subsequent link:exchange.html[Exchange]s then `oldExchange` and
  `newExchange` parameters are both not null.
  
  Example with Content Enricher EIP and no data
  
negative.code: }
  ----
  
  In the example above we use the xref:content-enricher.adoc[Content Enricher] 
  EIP using `pollEnrich`. The `newExchange` will be null in the
  situation we could not get any data from the "seda:foo" endpoint, and
  therefore the timeout was hit after 1 second. So if we need to do some
  special merge logic we would need to set `setAllowNullNewExchange=true`,
  so the `append` method will be invoked. If we do not do that then when
  the timeout was hit, then the append method would normally not be
  invoked, meaning the xref:content-enricher.adoc[Content Enricher] did
  not merge/change the message.
  
  In XML DSL you would configure the `strategyMethodAllowNull` option and
  