title: What cause org.hibernate.PropertyAccessException: Exception occurred inside setter
body: <p>What cause this exception, I can't manage to find out.</p>
  
  <pre><code>Request processing failed; nested exception is javax.persistence.PersistenceException: org.hibernate.PropertyAccessException: Exception occurred inside setter of my.Class
  </code></pre>
  
  <p>Root cause:</p>
  
  <pre><code>javax.persistence.PersistenceException: org.hibernate.PropertyAccessException: Exception occurred inside setter of my.Class
  </code></pre>
  
  <p>Code:</p>
  
  <pre><code>@ManyToMany(fetch = FetchType.EAGER)
  public void setTags(Set&lt;Tags&gt; tags) {
      this.tags.clear();
  
      for (Tag tag : tags) {
          addTag(tag);
      }
  }
  
  
  public boolean addTag(final Tag tag) {
      if (tags.contains(tag)) {
          return false;
      }
  
      return tags.add(tag);
  }
  </code></pre>
  
  <p>I initalize tags in the constructor:</p>
  
  <pre><code>tags = new HashSet&lt;Tag&gt;();
  </code></pre>
  
  <p>EDIT</p>
  
  <p>Exception from logging in setter method:</p>
  
  <pre><code>ax.persistence.PersistenceException: org.hibernate.PropertyAccessException: Exception occurred inside setter of com.mycompany.domain.Book.Tags
      at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1387) ~[hibernate-entitymanager-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.ejb.AbstractEntityManagerImpl.find(AbstractEntityManagerImpl.java:838) ~[hibernate-entitymanager-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.ejb.AbstractEntityManagerImpl.find(AbstractEntityManagerImpl.java:781) ~[hibernate-entitymanager-4.2.0.Final.jar:4.2.0.Final]
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:201304051638]
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) ~[na:201304051638]
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:201304051638]
      at java.lang.reflect.Method.invoke(Method.java:601) ~[na:1.7.0]
      at org.springframework.orm.jpa.SharedEntityManagerCreator$SharedEntityManagerInvocationHandler.invoke(SharedEntityManagerCreator.java:240) ~[spring-orm-3.1.4.RELEASE.jar:3.1.4.RELEASE]
      at $Proxy215.find(Unknown Source) ~[na:na]
      at com.mycompany.persistence.BookJpaRepository.get(BookJpaRepository.java:22) ~[classes/:na]
      at com.mycompany.service.BookService.getBook(BookService.java:44) ~[classes/:na]
      at com.mycompany.service.BookService$$FastClassByCGLIB$$d6b91ae6.invoke(&lt;generated&gt;) ~[BookService$$FastClassByCGLIB$$d6b91ae6.class:na]
      at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204) ~[spring-core-3.2.1.RELEASE.jar:3.2.1.RELEASE]
      at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:698) ~[spring-aop-3.2.1.RELEASE.jar:3.2.1.RELEASE]
      at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150) ~[spring-aop-3.2.1.RELEASE.jar:3.2.1.RELEASE]
      at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:110) ~[spring-tx-3.2.1.RELEASE.jar:3.2.1.RELEASE]
      at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172) ~[spring-aop-3.2.1.RELEASE.jar:3.2.1.RELEASE]
      at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:631) ~[spring-aop-3.2.1.RELEASE.jar:3.2.1.RELEASE]
      at com.mycompany.service.BookService$$EnhancerByCGLIB$$e6a4e1a3.getBook(&lt;generated&gt;) ~[BookService$$EnhancerByCGLIB$$e6a4e1a3.class:na]
      at com.mycompany.rest.controller.BookController.getFeedbackForBook(BookController.java:106) ~[classes/:na]
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:201304051638]
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) ~[na:201304051638]
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:201304051638]
      at java.lang.reflect.Method.invoke(Method.java:601) ~[na:1.7.0]
      at org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:219) ~[spring-web-3.2.1.RELEASE.jar:3.2.1.RELEASE]
      at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132) ~[spring-web-3.2.1.RELEASE.jar:3.2.1.RELEASE]
      at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104) ~[spring-webmvc-3.2.1.RELEASE.jar:3.2.1.RELEASE]
      at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:745) ~[spring-webmvc-3.2.1.RELEASE.jar:3.2.1.RELEASE]
      at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:686) ~[spring-webmvc-3.2.1.RELEASE.jar:3.2.1.RELEASE]
      at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80) ~[spring-webmvc-3.2.1.RELEASE.jar:3.2.1.RELEASE]
      at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:925) ~[spring-webmvc-3.2.1.RELEASE.jar:3.2.1.RELEASE]
      at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:856) ~[spring-webmvc-3.2.1.RELEASE.jar:3.2.1.RELEASE]
      at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:920) [spring-webmvc-3.2.1.RELEASE.jar:3.2.1.RELEASE]
      at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:816) [spring-webmvc-3.2.1.RELEASE.jar:3.2.1.RELEASE]
      at javax.servlet.http.HttpServlet.service(HttpServlet.java:668) [javax.servlet-api.jar:3.0.1]
      at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:801) [spring-webmvc-3.2.1.RELEASE.jar:3.2.1.RELEASE]
      at javax.servlet.http.HttpServlet.service(HttpServlet.java:770) [javax.servlet-api.jar:3.0.1]
      at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1550) [web-core.jar:3.1.2.1-SNAPSHOT]
      at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:281) [web-core.jar:3.1.2.1-SNAPSHOT]
      at org.apache.catalina.core.StandardContextValve.__invoke(StandardContextValve.java:175) [web-core.jar:3.1.2.1-SNAPSHOT]
      at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java) [web-core.jar:3.1.2.1-SNAPSHOT]
      at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:655) [web-core.jar:3.1.2.1-SNAPSHOT]
      at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:595) [web-core.jar:3.1.2.1-SNAPSHOT]
      at org.apache.catalina.core.StandardHostValve.__invoke(StandardHostValve.java:161) [web-core.jar:3.1.2.1-SNAPSHOT]
      at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java) [web-core.jar:3.1.2.1-SNAPSHOT]
      at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:331) [web-core.jar:3.1.2.1-SNAPSHOT]
      at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:231) [web-core.jar:3.1.2.1-SNAPSHOT]
      at com.sun.enterprise.v3.services.impl.ContainerMapper$AdapterCallable.call(ContainerMapper.java:317) [kernel.jar:3.1.2.1-SNAPSHOT]
      at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:195) [kernel.jar:3.1.2.1-SNAPSHOT]
      at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:860) [grizzly-http.jar:1.9.50]
      at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:757) [grizzly-http.jar:1.9.50]
      at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1056) [grizzly-http.jar:1.9.50]
      at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:229) [grizzly-http.jar:1.9.50]
      at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137) [grizzly-framework.jar:1.9.50]
      at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104) [grizzly-framework.jar:1.9.50]
      at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90) [grizzly-framework.jar:1.9.50]
      at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79) [grizzly-http.jar:1.9.50]
      at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54) [grizzly-framework.jar:1.9.50]
      at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59) [grizzly-framework.jar:1.9.50]
      at com.sun.grizzly.ContextTask.run(ContextTask.java:71) [grizzly-framework.jar:1.9.50]
      at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532) [grizzly-utils.jar:1.9.50]
      at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513) [grizzly-utils.jar:1.9.50]
      at java.lang.Thread.run(Thread.java:722) [na:1.7.0]
  Caused by: org.hibernate.PropertyAccessException: Exception occurred inside setter of com.mycompany.domain.Book.Tags
      at org.hibernate.property.BasicPropertyAccessor$BasicSetter.set(BasicPropertyAccessor.java:88) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.tuple.entity.AbstractEntityTuplizer.setPropertyValues(AbstractEntityTuplizer.java:710) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.tuple.entity.PojoEntityTuplizer.setPropertyValues(PojoEntityTuplizer.java:371) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.persister.entity.AbstractEntityPersister.setPropertyValues(AbstractEntityPersister.java:4499) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.engine.internal.TwoPhaseLoad.doInitializeEntity(TwoPhaseLoad.java:185) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.engine.internal.TwoPhaseLoad.initializeEntity(TwoPhaseLoad.java:137) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:1103) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.loader.Loader.processResultSet(Loader.java:960) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.loader.Loader.doQuery(Loader.java:910) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:341) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:311) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.loader.Loader.loadEntity(Loader.java:2111) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:82) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:72) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.persister.entity.AbstractEntityPersister.load(AbstractEntityPersister.java:3917) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.event.internal.DefaultLoadEventListener.loadFromDatasource(DefaultLoadEventListener.java:460) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.event.internal.DefaultLoadEventListener.doLoad(DefaultLoadEventListener.java:429) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.event.internal.DefaultLoadEventListener.load(DefaultLoadEventListener.java:206) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.event.internal.DefaultLoadEventListener.proxyOrLoad(DefaultLoadEventListener.java:262) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.event.internal.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:150) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.internal.SessionImpl.fireLoad(SessionImpl.java:1091) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.internal.SessionImpl.access$2000(SessionImpl.java:174) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.internal.SessionImpl$IdentifierLoadAccessImpl.load(SessionImpl.java:2473) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.internal.SessionImpl.get(SessionImpl.java:987) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.ejb.AbstractEntityManagerImpl.find(AbstractEntityManagerImpl.java:807) ~[hibernate-entitymanager-4.2.0.Final.jar:4.2.0.Final]
      ... 61 common frames omitted
  Caused by: java.lang.reflect.InvocationTargetException: null
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:201304051638]
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) ~[na:201304051638]
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:201304051638]
      at java.lang.reflect.Method.invoke(Method.java:601) ~[na:1.7.0]
      at org.hibernate.property.BasicPropertyAccessor$BasicSetter.set(BasicPropertyAccessor.java:65) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      ... 85 common frames omitted
  Caused by: java.lang.NullPointerException: null
      at org.hibernate.engine.internal.StatefulPersistenceContext.getLoadedCollectionOwnerOrNull(StatefulPersistenceContext.java:859) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.event.spi.AbstractCollectionEvent.getLoadedOwnerOrNull(AbstractCollectionEvent.java:75) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.event.spi.InitializeCollectionEvent.&lt;init&gt;(InitializeCollectionEvent.java:36) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.internal.SessionImpl.initializeCollection(SessionImpl.java:1846) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.collection.internal.AbstractPersistentCollection$4.doWork(AbstractPersistentCollection.java:549) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:234) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:545) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:124) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at org.hibernate.collection.internal.PersistentSet.iterator(PersistentSet.java:180) ~[hibernate-core-4.2.0.Final.jar:4.2.0.Final]
      at com.mycompany.domain.Book.setTags(Book.java:185) ~[classes/:na]
      ... 90 common frames omitted
  </code></pre>