I am testing the GridlockWithUI.java with mason.18.jar. An error of TimeSeriesChartGenerator is reported as follows: Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at sim.app.geo.gridlock.GridlockWithUI.start(GridlockWithUI.java:100) The problem is in the line of "trafficChart.removeAllSeries();". I guess the TimeSeriesChartGenerator object is not correctly constructed. Does anyone know about this problem? Thanks!