Проблема была в неуказанных типах у полей.

entityS.hbm.xml

<?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="Book" table="BOOK">
        <id name="id" type="string"></id>
        <property column="BOOK_NAME" name="name" type="string"/>
        <property column="BOOK_ISBN" name="isbn" type="string"/>
    </class>
</hibernate-mapping>