Restore default THcDriftChamber constructor.

src/THcDriftChamber.cxx

@@ -51,6 +51,16 @@ THcDriftChamber::THcDriftChamber(
   fHMSStyleChambers = 0;	// Default
 }
 
+//_____________________________________________________________________________
+THcDriftChamber::THcDriftChamber() :
+  THaSubDetector()
+{
+  // Constructor
+  fTrackProj = NULL;
+  fSpacePoints = NULL;
+  fIsInit = 0;
+
+}
 //_____________________________________________________________________________
 void THcDriftChamber::Setup(const char* name, const char* description)
 {

src/THcDriftChamber.h

@@ -55,6 +55,7 @@ public:
   //  friend class THaScCalib;
   void SetHMSStyleFlag(Int_t flag) {fHMSStyleChambers = flag;}
 
+  THcDriftChamber(); // for ROOT I/O
 protected:
   Int_t f;