Accessing message out of scope

Question

Hi all,
I have a message "Message_A" constructed inside the scope shape and being sent to the send port. Now when any exception occurs i need to log the details to the database. I have an exception handler with the expression in the construct message as
below
Excep_message(FILE.ReceivedFileName)=Message_A(FILE.ReceivedFileName);
I received the error "use of unconstructed message 'Message_A'" when compiling the project. For this error i constructed the message "Message_A" before the scope shape as below.
Message_A=null;
Message_A(BTS.Operation)="Operation";
Then i was able to compile the project without any error. When i deployed and the application exectued i got the below error.
xlang/s engine event log entry: Uncaught exception (see the 'inner exception' below) has suspended an instance of service 'Ibox.UNEDIFACT.COPARN.Orchestration.CoparnOrchestration_AEJEA(3f2f8342-08cd-6b69-c647-d13dc48b24ad)'.
The service instance will remain suspended until administratively resumed or terminated.
If resumed the instance will continue from its last persisted state and may re-throw the same unexpected exception.
InstanceId: 5bbb4a82-19ae-48bc-8bc0-b8c992088c68
Shape name: ConstructMessage_1
ShapeId: a849f763-3f7f-4bc3-bea2-9887fc3c7415
Exception thrown from: segment 1, progress 10
Inner exception: The part 'part' of message 'Message_A' contained a null value at the end of the construct block.
Exception type: NullPartException
Source: Microsoft.XLANGs.Engine
Target Site: Void ConstructionCompleteEvent(Boolean)
The following is a stack trace that identifies the location where the exception occured
   at Microsoft.XLANGs.Core.Part.ConstructionCompleteEvent(Boolean fKillUnderlyingPart)
   at Microsoft.XLANGs.Core.XMessage.ConstructionCompleteEvent(Boolean killUnderlyingPartWhenDirty)
   at Ibox.UNEDIFACT.COPARN.Orchestration.CoparnOrchestration_AEJEA.segment1(StopConditions stopOn)
   at Microsoft.XLANGs.Core.SegmentScheduler.RunASegment(Segment s, StopConditions stopCond, Exception& exp)
Kindly assist why the null error is being raised even when i have assigned the Message_A with a value.
Regards, Vivin.

Answer 1

You assigned Message_A with a null value, that's where the null error is raised! 
To assign Message_A with a value you will need to execute a mapping or assign it with a variable that contains a xmlDocument if your Message_A is a generic message.
Another question: why do you want a null Message_A on your messagebox? Is that the required behavior?
Be sure to also check following blog by Paole, it contains everything you need to know about processing and creating xlangmessages:
http://blogs.msdn.com/b/appfabriccat/archive/2010/06/23/4-different-ways-to-process-an-xlangmessage-within-an-helper-component-invoked-by-an-orchestration.aspx
Glenn Colpaert - Microsoft Integration MVP - Blog : http://blog.codit.eu