Mapping values from an idatacodable object using a flow service

I have this object in the pipeline:

 <idatacodable name="ExceptionTransitionInfo" javaclass="">
      <value name="ErrorMessage"></value>
      <value name="SourceStepId">S60</value>
      <value name="SourceStepIteration">4</value>
      <value name="ExceptionType">JoinTimeout</value>

And I would like to map the values from this object to a custom error message using a flow service.

Could anyone provide information about how to map values from an object like this? When I try to map from this object to an ExceptionTransitionInfo document type, I am not getting any data.

Thanks in advance!