#vulnerable code 
                              void print(int indentSpace) {
    StringBuilder builder = new StringBuilder();
    for (int i = 0; i < indentSpace; i++) {
      builder.append(" ");
    }
    builder.append(this.toString());
    System.out.println(builder.toString());
    
    for (QueryExecutionNode dep : dependents) {
      dep.print(indentSpace + 2);
    }
  } 
                            #location 6 
                            #vulnerability type THREAD_SAFETY_VIOLATION
#fixed code
                              void addParent(QueryExecutionNode parent) {
    parents.add(parent);
  }