Flat file schema question

Hi there,

Does anybody know how to perserve empty string in flat file schema? Here is my senario, we created a flat file schema for EDI X12 861 transaction and all the elements are defined as string type without restrictions (no minimum/maximum length ect…). We have some reason not using EDI adapter or Covast but it's out of the scope.

Moving forward to next stage, I created a simple pass through solultion with a custom flat file pipeline to receive the following inbound message, and have a send port subscribe it and drop the outbound message to a folder. While comparing the inbound and outbound messages, I found they are all same except the empty string in the header was stripped out by BizTalk.

My question is, is there a property or annotation on schema level that I can use to force BizTalk not trim out the empty string?

Inbound message:

ISA*00*          *00*          *ZZ*058020496RP    *01*081466849      *061229*0153*U*00300*000060502*0*P*>~GS*RC*058020496RP*TURNKEY*061229*01533201*9154*X*003050~ST*861*000024993~BRA*0000009732*061229*ZZ*1*0153~REF*WR*0000009732~DTM*050*061229*17330000*20~TD5*2*BURA*M~N1*SF*92*2070024~N1*ST*92*4500~RCD***70000*EA*07~SN1*70000*EA~LIN*02*BP*112-00131*ZZ*PO~PID*F**WORD/EXCEL 2007 W32 JA CD PKG W/IME~REF*PO*6000086289~CTT*1*70000~SE*14*000024993~GE*1*9154~IEA*1*000060502~

Outbound message:

ISA*00**00**ZZ*058020496RP*01*081466849*061229*0153*U*00300*000060502*0*P*>~GS*RC*058020496RP*TURNKEY*061229*01533201*9154*X*003050~ST*861*000024993~BRA*0000009732*061229*ZZ*1*0153*~REF*W?R*0000009732***~DTM*050*061229*17330000*20*~TD5*2*BURA*M*~N1*SF*92*2070024~N1*ST*92*4500~RCD***70000*EA*07~SN1*70000*EA~LIN*02*B?P*112-00131*ZZ*PO~PID*F**WORD/EXCEL 2007 W32 JA CD PKG W/IME***~REF*PO*6000086289~CTT*1*70000~SE*14*000024993~GE*1*9154~IEA*1*000060502~

Thanks in advance!