There a is problem when an exception occurs in org.hibernate.tool.hbm2ddl.DatabaseMetadata#initSequences:

Statement statement = null;
ResultSet rs = null;
try {
	statement = connection.createStatement();
	rs = statement.executeQuery(sql);

	while ( rs.next() ) {
		sequences.add( rs.getString(1).toLowerCase().trim() );
	}
}
finally {
	rs.close();
	statement.close();
}

If rs = statement.executeQuery(sql) fails, then in finally block we try to invoke close() method on rs object, which is still null. According to JLS §14.20.2.:

If the finally block completes abruptly for reason S, then the try statement completes abruptly for reason S (and the throw of value V is discarded and forgotten).

So the reason why statement.executeQuery(sql) failed is discarded and forgotten and NullPointerException is thrown. That makes it really hard to debug.

I found this bug when I in my Spring application I've tried to connect do DERBY database using H2Dialect:

<jdbc:embedded-database id="dataSource" type="DERBY"/>

<bean id="sessionFactory" class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">
    <property name="dataSource" ref="dataSource"/>
    <property name="packagesToScan" value="hello"/>
    <property name="hibernateProperties">
        <props>
            <prop key="hibernate.hbm2ddl.auto">update</prop>
            <prop key="hibernate.dialect">org.hibernate.dialect.H2Dialect</prop>
        </props>
    </property>
</bean>