<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
   "-//Hibernate/Hibernate Mapping DTD 2.0//EN"
   "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">
<hibernate-mapping
   package="somepackage.group.model">

   <class name="Group" table="contactGroup" discriminator-value="N">      
      <id name="id" column="Group_ID">
         <generator class="native"/>
      </id>      
      <version name="lastChange" type="timestamp"/>      
      
      <property name="name" not-null="true">            
         <column name="name" sql-type="varchar(50)" />
      </property>
      
      <property name="type" column="group_type" type="somepackage.group.model.GroupType" not-null="true"/>
      
      <bag name="members" table="group_member" lazy="true" inverse="false">
         <key column="GROUP_ID"/>
         <many-to-many class="Contact" column="CONTACT_ID" />
      </bag>
      
      <many-to-one name="subscriber" column="Subscriber_ID" not-null="true"/>
      
   </class>   
</hibernate-mapping>

<bag name="groups" lazy="true" table="group_member" inverse="true">
         <key column="CONTACT_ID"/>
         <many-to-many class="Group" column="GROUP_ID"/>
</bag>

java.lang.NullPointerException
   at net.sf.hibernate.collection.Bag.toString(Bag.java:483)

lazy="false"

SamSessionFactory.getSession().iterate("from Group");