title: i use kotlin coroutines nullpointExecption but not show just crash no log
body: <p>i use kotlin coroutines encounter nullpointExecption but not show me just crashed no log to print 
  i code like this:</p>
  
  <pre><code>  val job = GlobalScope.launch(Dispatchers.IO) {
                      val files = File(path).listFiles(videoFileFilter)
                      Log.d("yanghua", "${files.size}")
                      for (file in files) {
                          Log.d("yanghua", file.absolutePath)
                      }
  
  
              }
  </code></pre>
  
  <p>the files is null because there no file matched,than files.size is nullpoint exception,but app crashed but not show me the exception,
  and I use thread instead,it will be crash too but show me where the Exception,like this</p>
  
  <pre><code>java.lang.RuntimeException: Unable to start activity ComponentInfo{com.huayang.localplayer/com.huayang.localplayer.FileExplorActivity}: java.lang.NullPointerException: Attempt to get length of null array
  </code></pre>
  
  <p>I don't know why? Anybody knows?</p>