doubleが0または0.0の場合異常

package com;

import java.util.Map;   

import org.apache.struts2.util.StrutsTypeConverter;   

public class DoubleConvert extends StrutsTypeConverter {   

    @SuppressWarnings("unchecked")

	@Override  

    public Object convertFromString(Map context, String[] values, Class toClass) {   

        if (Double.class == toClass) {   

             String doubleStr = values[0];   

             Double d = Double.parseDouble(doubleStr);   

            return d;   

         }   

        return 0;   

     }   

  

    @SuppressWarnings("unchecked")

	@Override  

    public String convertToString(Map context, Object o) {   

        return o.toString();   

     }   

}