Program: 173683
Project: 173683
Buggy source:
public static MergeResult mergeEdges(NetworkEdge edgeA,NetworkEdge edgeB){
  log.info("String_Node_Str" + edgeA.toFullInfoString() + "String_Node_Str"+ edgeB.toFullInfoString());
  NetworkVertex sourceA=edgeA.getSource();
  NetworkVertex targetA=edgeA.getTarget();
  NetworkVertex sourceB=edgeB.getSource();
  NetworkVertex targetB=edgeB.getTarget();
  NetworkVertex newSource, newTarget, vertex=null;
  boolean reverseA=false, reverseB=false;
  if (sourceA == sourceB) {
    newSource=targetA;
    newTarget=targetB;
    vertex=sourceA;
    reverseA=true;
  }
 else   if (sourceA == targetB) {
    newSource=targetA;
    newTarget=sourceB;
    vertex=sourceA;
    reverseA=true;
    reverseB=true;
  }
 else   if (targetA == sourceB) {
    newSource=sourceA;
    newTarget=targetB;
    vertex=targetA;
  }
 else   if (targetA == targetB) {
    newSource=sourceA;
    newTarget=sourceB;
    vertex=targetA;
    reverseB=true;
  }
 else {
    return null;
  }
  log.info("String_Node_Str" + newSource + "String_Node_Str"+ newTarget+ "String_Node_Str"+ vertex);
  int distance=edgeA.getDistance() + edgeB.getDistance();
  List<NetworkVertex> hiddenVertexes=new ArrayList<NetworkVertex>();
  List<NetworkVertex> hiddenA=edgeA.getHiddenVertexes();
  if (reverseA) {
    hiddenA=new ArrayList<NetworkVertex>(hiddenA);
    Collections.reverse(hiddenA);
  }
  List<NetworkVertex> hiddenB=edgeB.getHiddenVertexes();
  if (reverseB) {
    hiddenB=new ArrayList<NetworkVertex>(hiddenB);
    Collections.reverse(hiddenB);
  }
  hiddenVertexes.addAll(hiddenA);
  hiddenVertexes.add(vertex);
  hiddenVertexes.addAll(hiddenB);
  NetworkEdge newEdge=new NetworkEdge(newSource,newTarget,true,distance,hiddenVertexes);
  log.info("String_Node_Str" + newEdge.toFullInfoString());
  return new MergeResult(newEdge,vertex);
}

Fixed version (ground truth):
public static MergeResult mergeEdges(NetworkEdge edgeA,NetworkEdge edgeB){
  log.info("String_Node_Str" + edgeA.toFullInfoString() + "String_Node_Str"+ edgeB.toFullInfoString());
  NetworkVertex sourceA=edgeA.getSource();
  NetworkVertex targetA=edgeA.getTarget();
  NetworkVertex sourceB=edgeB.getSource();
  NetworkVertex targetB=edgeB.getTarget();
  NetworkVertex newSource, newTarget, vertex=null;
  boolean reverseA=false, reverseB=false;
  if (sourceA == sourceB) {
    newSource=targetA;
    newTarget=targetB;
    vertex=sourceA;
    reverseA=true;
  }
 else   if (sourceA == targetB) {
    newSource=targetA;
    newTarget=sourceB;
    vertex=sourceA;
    reverseA=true;
    reverseB=true;
  }
 else   if (targetA == sourceB) {
    newSource=sourceA;
    newTarget=targetB;
    vertex=targetA;
  }
 else   if (targetA == targetB) {
    newSource=sourceA;
    newTarget=sourceB;
    vertex=targetA;
    reverseB=true;
  }
 else {
    return null;
  }
  log.info("String_Node_Str" + newSource + "String_Node_Str"+ newTarget+ "String_Node_Str"+ vertex);
  int distance=edgeA.getDistance() + edgeB.getDistance();
  List<NetworkVertex> hiddenVertexes=new ArrayList<NetworkVertex>();
  List<NetworkVertex> hiddenA=edgeA.getHiddenVertices();
  if (reverseA) {
    hiddenA=new ArrayList<NetworkVertex>(hiddenA);
    Collections.reverse(hiddenA);
  }
  List<NetworkVertex> hiddenB=edgeB.getHiddenVertices();
  if (reverseB) {
    hiddenB=new ArrayList<NetworkVertex>(hiddenB);
    Collections.reverse(hiddenB);
  }
  hiddenVertexes.addAll(hiddenA);
  hiddenVertexes.add(vertex);
  hiddenVertexes.addAll(hiddenB);
  NetworkEdge newEdge=new NetworkEdge(newSource,newTarget,true,distance,hiddenVertexes);
  log.info("String_Node_Str" + newEdge.toFullInfoString());
  return new MergeResult(newEdge,vertex);
}