Exception in implicit renderer when running simple scala test

[afewnotes]

Build:
| formattedShaVersion-0.9.0-SNAPSHOT-e85f700a6fb92129aff5b17e201e37db5ae57a78-SNAPSHOT | sbtVersion-0.13.15 | scalaVersion-2.11.8 | sparkNotebookVersion-0.9.0-SNAPSHOT | viewer-false | hadoopVersion-2.7.3 | jets3tVersion-0.7.1 | jlineDef-(jline,2.12) | sparkVersion-2.1.1 | withHive-false |.

System: CentOS7

Code sample

import scala.xml._
val html = XML.loadFile("some.html")
import scala.xml.transform._
val rule1 = new RewriteRule {
  override def transform(n: Node) = n match {
    case e @ <img>{_*}</img> if (e.attribute("alt") == None) => e.asInstanceOf[Elem] % Attribute(null, "alt", "TODO", Null)
    case _ => n
  }
}
new RuleTransformer(rule1).transform(html)

The result of above test was printed rightly, with the exception below.(but nothing throwed in the server's log)
And I created a fresh new notebook and run this test, the same error happened.
looks like it run into some strange dead loop?

Exception (more than 1k lines)

Exception in implicit renderer:
notebook.front.widgets.Utils$class.toJson(Utils.scala:45)
notebook.front.widgets.charts.Chart.toJson(Chart.scala:34)
notebook.front.widgets.Utils$$anonfun$3.apply(Utils.scala:63)
notebook.front.widgets.Utils$$anonfun$3.apply(Utils.scala:63)
scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:234)
scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:234)
scala.collection.Iterator$class.foreach(Iterator.scala:893)
scala.collection.AbstractIterator.foreach(Iterator.scala:1336)
scala.collection.IterableLike$class.foreach(IterableLike.scala:72)
scala.collection.AbstractIterable.foreach(Iterable.scala:54)
scala.collection.TraversableLike$class.map(TraversableLike.scala:234)
scala.collection.AbstractTraversable.map(Traversable.scala:104)
notebook.front.widgets.Utils$class.toJson(Utils.scala:63)
notebook.front.widgets.charts.Chart.toJson(Chart.scala:34)
notebook.front.widgets.Utils$$anonfun$3.apply(Utils.scala:63)
notebook.front.widgets.Utils$$anonfun$3.apply(Utils.scala:63)
scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:234)
scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:234)
scala.collection.Iterator$class.foreach(Iterator.scala:893)
scala.collection.AbstractIterator.foreach(Iterator.scala:1336)
scala.collection.IterableLike$class.foreach(IterableLike.scala:72)
scala.collection.AbstractIterable.foreach(Iterable.scala:54)
scala.collection.TraversableLike$class.map(TraversableLike.scala:234)
scala.collection.AbstractTraversable.map(Traversable.scala:104)
notebook.front.widgets.Utils$class.toJson(Utils.scala:63)
notebook.front.widgets.charts.Chart.toJson(Chart.scala:34)
notebook.front.widgets.Utils$$anonfun$3.apply(Utils.scala:63)
notebook.front.widgets.Utils$$anonfun$3.apply(Utils.scala:63)
scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:234)
scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:234)
scala.collection.Iterator$class.foreach(Iterator.scala:893)
......
......
scala.collection.AbstractIterator.foreach(Iterator.scala:1336)
scala.collection.IterableLike$class.foreach(IterableLike.scala:72)
scala.collection.AbstractIterable.foreach(Iterable.scala:54)
scala.collection.TraversableLike$class.map(TraversableLike.scala:234)
scala.collection.AbstractTraversable.map(Traversable.scala:104)
notebook.front.widgets.Utils$class.toJson(Utils.scala:63)
notebook.front.widgets.charts.Chart.toJson(Chart.scala:34)
notebook.front.widgets.Utils$$anonfun$3.apply(Utils.scala:63)
notebook.front.widgets.Utils$$anonfun$3.apply(Utils.scala:63)
scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:234)
scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:234)
scala.collection.Iterator$class.foreach(Iterator.scala:893)
scala.collection.AbstractIterator.foreach(Iterator.scala:1336)
scala.collection.IterableLike$class.foreach(IterableLike.scala:72)
scala.collection.AbstractIterable.foreach(Iterable.scala:54)
scala.collection.TraversableLike$class.map(TraversableLike.scala:234)
scala.collection.AbstractTraversable.map(Traversable.scala:104)
notebook.front.widgets.Utils$class.toJson(Utils.scala:63)
notebook.front.widgets.charts.Chart.toJson(Chart.scala:34)
notebook.front.widgets.Utils$$anonfun$3.apply(Utils.scala:63)
notebook.front.widgets.Utils$$anonfun$3.apply(Utils.scala:63)