Program: 53533
Project: 53533
Buggy source:
/** 
 * Tighten based on assignment, and for parameters, callArgs as well.
 */
private void tighten(JVariable x){
  if (!(x.getType() instanceof JReferenceType)) {
    return;
  }
  JReferenceType refType=(JReferenceType)x.getType();
  if (refType == typeNull) {
    return;
  }
  if (!program.typeOracle.isInstantiatedType(refType)) {
    x.setType(typeNull);
    madeChanges();
    return;
  }
  JReferenceType leafType=getSingleConcreteType(refType);
  if (leafType != null) {
    x.setType(leafType);
    madeChanges();
    return;
  }
  List<JReferenceType> typeList=new ArrayList<JReferenceType>();
  if ((x instanceof JField) && !x.hasInitializer()) {
    typeList.add(typeNull);
  }
  Collection<JExpression> myAssignments=assignments.get(x);
  if (myAssignments != null) {
    for (    JExpression expr : myAssignments) {
      JType type=expr.getType();
      if (!(type instanceof JReferenceType)) {
        return;
      }
      typeList.add((JReferenceType)type);
    }
  }
  if (x instanceof JParameter) {
    Collection<JParameter> myParams=paramUpRefs.get(x);
    if (myParams != null) {
      for (      JParameter param : myParams) {
        typeList.add((JReferenceType)param.getType());
      }
    }
  }
  JReferenceType resultType;
  if (!typeList.isEmpty()) {
    resultType=program.generalizeTypes(typeList);
    resultType=program.strongerType(refType,resultType);
  }
 else {
    if (x instanceof JParameter) {
      resultType=refType;
    }
 else {
      resultType=typeNull;
    }
  }
  if (x.getType() != resultType) {
    x.setType(resultType);
    madeChanges();
  }
}

Fixed version (ground truth):
/** 
 * Tighten based on assignment, and for parameters, callArgs as well.
 */
private void tighten(JVariable x){
  if (!(x.getType() instanceof JReferenceType)) {
    return;
  }
  JReferenceType refType=(JReferenceType)x.getType();
  if (program.typeOracle.isJsType(refType)) {
    return;
  }
  if (refType == typeNull) {
    return;
  }
  if (!program.typeOracle.isInstantiatedType(refType)) {
    x.setType(typeNull);
    madeChanges();
    return;
  }
  JReferenceType leafType=getSingleConcreteType(refType);
  if (leafType != null) {
    x.setType(leafType);
    madeChanges();
    return;
  }
  List<JReferenceType> typeList=new ArrayList<JReferenceType>();
  if ((x instanceof JField) && !x.hasInitializer()) {
    typeList.add(typeNull);
  }
  Collection<JExpression> myAssignments=assignments.get(x);
  if (myAssignments != null) {
    for (    JExpression expr : myAssignments) {
      JType type=expr.getType();
      if (!(type instanceof JReferenceType)) {
        return;
      }
      typeList.add((JReferenceType)type);
    }
  }
  if (x instanceof JParameter) {
    Collection<JParameter> myParams=paramUpRefs.get(x);
    if (myParams != null) {
      for (      JParameter param : myParams) {
        typeList.add((JReferenceType)param.getType());
      }
    }
  }
  JReferenceType resultType;
  if (!typeList.isEmpty()) {
    resultType=program.generalizeTypes(typeList);
    resultType=program.strongerType(refType,resultType);
  }
 else {
    if (x instanceof JParameter) {
      resultType=refType;
    }
 else {
      resultType=typeNull;
    }
  }
  if (x.getType() != resultType) {
    x.setType(resultType);
    madeChanges();
  }
}