[Hibernate] Não consigo deletar

public class Item {

private Long idItem;
private String titulo;
private String subTitulo;
private String localizacao;
private TipoMaterial tipoMaterial;
private String editora;
private Date dataPublicacao;
private String edicao;
private Boolean script;
private Boolean acompanhadoDeAtividade;
private String dadosTecnicos;
private Classificacao classificacao;
private String sinopse;
private Idioma idioma;
private Status status;

private Set autores = new HashSet();
private Set capitulos = new HashSet();
private Set tagsItens = new HashSet();

//aqui vão: contrutor, setters e getters...

<hibernate-mapping>

	<class name="model.Item" table="item">
	
            <id name="idItem">
            	<generator class="native"/>
	    </id>
	    
	    <property name="titulo" not-null="true"/>
	    <property name="subTitulo"/>
	    <property name="localizacao"/>
	    
	    <many-to-one class="model.TipoMaterial" name="tipoMaterial" column="idTipoMaterial" foreign-key="FK_idTipoMaterial" not-null="true"/>
	    
	    <set name="autores" table="Item_Autores">
			<key column="idItem"/>
			<many-to-many column="idAutor" class="model.Autor"/>
		</set>
		
	    <property name="editora"/>
	    <property name="dataPublicacao" type="timestamp" />
	    <property name="edicao"/>
	    <property name="script" type="yes_no"/>
	    <property name="acompanhadoDeAtividade" type="yes_no"/>
	    <property name="dadosTecnicos"/>
	    
	    <many-to-one class="model.Classificacao" name="classificacao" column="idClassificacao" foreign-key="FK_idClassificacao" not-null="true"/>
	    
	    <property name="sinopse"/>
	    
	    <many-to-one class="model.Idioma" name="idioma" column="idIdioma" foreign-key="FK_idIdioma" not-null="true"/>
	    <many-to-one class="model.Status" name="status" column="idStatus" foreign-key="FK_idStatus" not-null="true"/>
	    
		<set name="capitulos" table="capitulo" lazy="true" cascade="all-delete-orphan">
            	<key column="idItem" foreign-key="FK_idItem"/>
            	<one-to-many class="model.Capitulo"/>
		</set>
		
		<set name="tagsItens" table="Item_TagItens">
			<key column="idItem"/>
			<many-to-many column="idTagItem" class="model.TagItem"/>
		</set>
	
	</class>

</hibernate-mapping>

//Abre a sessão
Session sessao = HibernateUtil.getSessionFactory().getCurrentSession();
sessao.beginTransaction(); 

//Pega os parametros passados e armazena em objeto
ItemManager itemManager = new ItemManager();
Item currentItem = (Item) sessao.load(Item.class, (long) Long.parseLong(request.getParameter("idItem")));

//Deleta objeto
sessao.delete(currentItem);
sessao.getTransaction().commit();
HibernateUtil.getSessionFactory().close();
response.sendRedirect("../?pag=viewItem&mensagem=31");

exception

org.apache.jasper.JasperException: An exception occurred processing JSP page /includes/deleteItem.jsp at line 14

11:     
12: 	//Deleta objeto
13: 	sessao.delete(currentItem);
14: 	sessao.getTransaction().commit();
15: 	HibernateUtil.getSessionFactory().close();
16: 	response.sendRedirect("../?pag=viewItem&mensagem=31");
17: %>


Stacktrace:
	org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:505)
	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:416)
	org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:337)
	org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

root cause

org.hibernate.exception.ConstraintViolationException: Could not execute JDBC batch update
(...)

root cause

java.sql.BatchUpdateException: Column 'idItem' cannot be null
(...)