could not initialize proxy - no Session

08:37:15,203 ERROR LazyInitializationException:19 - could not initialize proxy - no Session
org.hibernate.LazyInitializationException: could not initialize proxy - no Session
at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:57)
at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:111)
at org.hibernate.proxy.pojo.cglib.CGLIBLazyInitializer.invoke(CGLIBLazyInitializer.java:150)
at com.bjsxt.oa.model.Orgnization$$EnhancerByCGLIB$$8b056ba1.getParent(<generated>)
at com.bjsxt.oa.web.actions.OrgAction.execute(OrgAction.java:64)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:404)
at com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:267)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:229)
at com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:221)
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:86)
package com.bjsxt.oa.model;
import java.util.Set;
public class Orgnization {
private int id;
private String name;
private String sn;
private String description;
private Orgnization parent;
private Set children;
.....
}hibernate-mapping>
  <class table="t_orgnization" name="com.bjsxt.oa.model.Orgnization">
  <id name="id">
  <generator class="native"/>
  </id>
  <property name="name"/>
  <property name="sn"/>
  <property name="description"/>
    
  <many-to-one column="pid" name="parent" />
  <set lazy="false" inverse="true" name="children">
  <key column="pid"/>
  <one-to-many class="com.bjsxt.oa.model.Orgnization" />
  </set>
  </class>
</hibernate-mapping>if(parentId != 0){
     Orgnization org = orgManager.findOrg(parentId);
     Orgnization parent = org.getParent();（执行这句开始出错） 
     if(parent != null){
        ppid = parent.getId();
     }
   }
 request.put("ppid", ppid);