Random exception while doing data quantiles

[mihaibudiu]

TableTarget.getDataQuantiles()
java.lang.NullPointerException: Value should not be null
	at org.hillview.utils.Converters.checkNull(Converters.java:74)
	at org.hillview.sketches.highorder.MultiPostprocessedSketch.postProcess(MultiPostprocessedSketch.java:55)
	at org.hillview.sketches.highorder.MultiPostprocessedSketch.postProcess(MultiPostprocessedSketch.java:37)
	at org.hillview.RpcTarget$CompleteSketchResultObserver.onCompleted(RpcTarget.java:342)
	at org.hillview.RpcTarget.runObservedSketch(RpcTarget.java:424)
	at org.hillview.RpcTarget.runCompleteSketch(RpcTarget.java:444)
	at org.hillview.targets.TableTarget.getDataQuantiles(TableTarget.java:245)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.hillview.RpcTarget.execute(RpcTarget.java:137)
	at org.hillview.RpcServer.lambda$execute$2(RpcServer.java:131)
	at org.hillview.RpcObjectManager$1.action(RpcObjectManager.java:154)
	at org.hillview.RpcObjectManager.executeAction(RpcObjectManager.java:138)
	at org.hillview.RpcObjectManager.when(RpcObjectManager.java:157)
	at org.hillview.RpcServer.execute(RpcServer.java:127)
	at org.hillview.RpcServer.onMessage(RpcServer.java:120)
	at sun.reflect.GeneratedMethodAccessor23.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)