解析C#中断言与异常的应用方式及异常处理的流程控制

public void WriteSnapShot(string fileName, IEnumerable items)
    {
      string format = "{0}\t{1}\t{2}\t{3}\t{4}\t{5}";
      using (FileStream fs = new FileStream(fileName, FileMode.Create))
      {
        using (StreamWriter sw = new StreamWriter(fs, Encoding.Unicode))
        {
　　　　　　　　　　　...
          foreach (var item in items)
          {
            sw.WriteLine(string.Format(format, new object[]{
              item.dealMan,
              item.version,
              item.priority,
              item.bugStatus,
              item.bugNum,
              item.description}));
          }
          sw.Flush();
        }
      }
    }

public Entities.SimpleBugInfo GetSimpleBugInfo(string bugNum)
    {

      var selector = DependencyFactory.Resolve();

      var list = selector.Return(
        reader => new Entities.SimpleBugInfo
        {
          bugNum = reader["bugNum"].ToString(),
          dealMan = reader["dealMan"].ToString(),
          description = reader["description"].ToString(),
          size = Convert.ToInt32(reader["size"]),
          fired = Convert.ToInt32(reader["fired"]),
        },
        "select * from bugInfo",
        new WhereClause(bugNum, "bugNum"));

      Trace.Assert(list != null);
      
      if (list.Count == 0)
        return null;
      else
        return list[0];

    }

If(list == null)
{
  throw new NullReferenceException();
}

if(list == null || list.Count == 0)
{
  return null;
}
else
{
  return list[0];
}

try
          {
            foreach (var lockGroup in lockGroups)
            {
 
              ...
 
              foreach (var newlock in lockGroup.ToArray())
              {
                ...
                if (diningBlocks.Exists(n => testLockRange.IsOverlapped(n.StartTime, n.EndTime)))
                {
                  status = LockStatus.InResourceBlock;
                  throw new LockException();
                }
 
                var diningAvail = availabilities.Find(n => n.Time == newlock.StartTime.TimeOfDay);
                if (diningAvail == null)
                {
                  status = LockStatus.Failed;
                  throw new LockException();
                }
 
                ...
                 
                if (newLockQuantity > diningAvail.MaxAvail && !canOverrideLock.AllowOverBook)
                {
                  status = LockStatus.Override;
                  throw new LockException();
                }
                else if (newLockQuantity + reservedQuantity + currentLockedAvail > diningAvail.MaxAvail && !canOverrideLock.AllowOverBook)
                {
                  status = LockStatus.Override;
                  throw new LockException();
                }
 
                ...
              }
            }
          }
          catch (LockException)
          {
            return new DiningLock[] { };
          }