null check for:
ava.lang.NullPointerException 
     at
com.servoy.j2db.server.headlessclient.dataui.WebCellBasedView.getSelectedIndexes(WebCellBasedView.java:4905) 
     at
com.servoy.j2db.server.headlessclient.dataui.WebCellBasedView.access$49(WebCellBasedView.java:4902) 
     at
com.servoy.j2db.server.headlessclient.dataui.WebCellBasedView$ScrollBehavior.scrollViewPort(WebCellBasedView.java:5351) 
     at
com.servoy.j2db.server.headlessclient.dataui.WebCellBasedView.scrollViewPort(WebCellBasedView.java:5213) 
     at
com.servoy.j2db.server.headlessclient.dataui.WebCellBasedView.onBeforeRender(WebCellBasedView.java:3027) 
     at
org.apache.wicket.Component.internalBeforeRender(Component.java:1069)
null check