<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="br.com.teste.model.Categoria" table="CATEGORIA">
        <id name="id" type="java.lang.Long">
            <column name="ID" precision="12" scale="0" />
            <generator class="sequence">
               <param name="sequence">SQ_CATEGORIA</param>
            </generator>
        </id>
        <property name="nome" type="java.lang.String">
            <column name="NOME" length="100" not-null="true" />
        </property>
        <set name="produtos" inverse="true">
            <key column="CATEGORIA_ID" />
            <one-to-many class="br.com.teste.model.Produto" />
        </set>
    </class>
</hibernate-mapping>

      Categoria categoria = new Categoria();
      categoria.setId(Long.valueOf("50"));
      
      Session s = HibernateSessionFactory.getSession();
      
      Transaction tx = s.beginTransaction();
      s.delete(categoria);
      tx.commit();
      
      s.close();

org.hibernate.PropertyValueException: not-null property references a null or transient value: br.com.teste.model.Categoria.nome
   at org.hibernate.engine.Nullability.checkNullability(Nullability.java:72)