Data Handlers are chained together too early - resulting in some 'nulls'

There is a problem with these two methods:

https://github.com/apiman/apiman/blob/master/gateway/engine/core/src/main/java/io/apiman/gateway/engine/policy/IDataPolicy.java#L41

https://github.com/apiman/apiman/blob/master/gateway/engine/core/src/main/java/io/apiman/gateway/engine/policy/IDataPolicy.java#L50

These methods are being called when the Chains are first created, prior to the ServiceRequest and ServiceResponse objects being created. This results in both being NULL when the above methods are invoked.

Can we perhaps defer chaining together the data handlers until later so that they are not null?

To reproduce, put a breakpoint in SimpleDataPolicy's getRequestDataHandler() and getResponseDataHandler() methods and run the SimpleDataPolicyTest junit test. When they get hit, you'll notice that both those params are null.