also add check for null for straight tracking

Author: tongtongcao

reconstruction/dc/src/main/java/org/jlab/rec/dc/track/TrackCandListFinder.java

@@ -926,11 +926,13 @@ private List<Track> findStraightTracks(CrossList crossList, DCGeant4Factory DcDe
                             cand.set_Id(cands.size() + 1);
                             cand.set_CovMat(kFZRef.finalStateVec.CM);
 
-                            Point3D VTCS = cand.get(cand.size()-1).getCoordsInTiltedSector(cand.get_Vtx0().x(), cand.get_Vtx0().y(), cand.get_Vtx0().z());
-                            double deltaPathToVtx =  kFZRef.getDeltaPathToVtx(cand.get(cand.size()-1).get_Sector(), VTCS.z());
+                            if (cand.get_Vtx0() != null) {
+                                Point3D VTCS = cand.get(cand.size()-1).getCoordsInTiltedSector(cand.get_Vtx0().x(), cand.get_Vtx0().y(), cand.get_Vtx0().z());
+                                double deltaPathToVtx =  kFZRef.getDeltaPathToVtx(cand.get(cand.size()-1).get_Sector(), VTCS.z());
 
-                            List<org.jlab.rec.dc.trajectory.StateVec> kfStateVecsAlongTrajectory = setKFStateVecsAlongTrajectory(kFZRef, deltaPathToVtx);
-                            cand.setStateVecs(kfStateVecsAlongTrajectory);
+                                List<org.jlab.rec.dc.trajectory.StateVec> kfStateVecsAlongTrajectory = setKFStateVecsAlongTrajectory(kFZRef, deltaPathToVtx);
+                                cand.setStateVecs(kfStateVecsAlongTrajectory);
+                            }
 
                             // add candidate to list of tracks	
                             cands.add(cand);
@@ -1104,14 +1106,14 @@ private List<Track> findCurvedTracks(CrossList crossList, DCGeant4Factory DcDete
                                         fitStateVec.getZ(),
                                         DcDetector, dcSwim);
 
-                                Point3D vtx = cand.get_Vtx0();
-                                if (vtx != null) {
+                                if (cand.get_Vtx0() != null) {
                                     Point3D VTCS = cand.get(cand.size()-1).getCoordsInTiltedSector(cand.get_Vtx0().x(), cand.get_Vtx0().y(), cand.get_Vtx0().z());
                                     double deltaPathToVtx =  kFZRef.getDeltaPathToVtx(cand.get(cand.size()-1).get_Sector(), VTCS.z());
 
                                     List<org.jlab.rec.dc.trajectory.StateVec> kfStateVecsAlongTrajectory = setKFStateVecsAlongTrajectory(kFZRef, deltaPathToVtx);
                                     cand.setStateVecs(kfStateVecsAlongTrajectory);
                                 }
+                                
                                 // add candidate to list of tracks
                                 if (cand.fit_Successful = true) {
                                     cands.add(cand);