[net.sf.jasperreports.engine.data.JRBeanCollectionDataSource cannot be cast to java.lang.Boolean error]

I am getting an exception( Exception in thread "main" java.lang.ClassCastException: net.sf.jasperreports.engine.data.JRBeanCollectionDataSource cannot be cast to java.lang.Boolean )  while creating a report(Bar Grap) in iReport. I am passing JRBeanCollectionDataSource object through map as follow.

1st I have created POJO class then created object of that POJO class inserted them in a list. Then created JRBeanCollectionDataSource from that list as follow

JRBeanCollectionDataSource chartDataSource = new JRBeanCollectionDataSource(list);

and passing that parameter through hashmap 

HashMap<String, Object> parameters = new HashMap<String, Object>(); 

 parameters.put("chartDataSource", chartDataSource); 

In iReports I have created parameter with name="chartDataSource" and type="net.sf.jasperreports.engine.data.JRBeanCollectionDataSource" created fields as created in  the POJO (All fields are of String type).

But while generating Graph in iReport getting exception "Exception in thread "main" java.lang.ClassCastException: net.sf.jasperreports.engine.data.JRBeanCollectionDataSource cannot be cast to java.lang.Boolean "

Please help.