ModelMapper: mapping abstract classes during runtime

I am using ModelMapper Framework (http://modelmapper.org/) for mapping objects in Java. I have encountered a problem while mapping concrete classes (DTO to Entites) containing abstract classes.

Example: Task has a list of AbstractItems.
AbstractItems are Question and Criteria.

public class TaskDTO {
   ...
   private List<AbstractItemDTO> items;
}

Mapping method:

// task is an TaskDTO object
return getModelMapper().map(task, TaskEntity.class);

ModelMapper tries to create a new instance of AbstractItem, which throws an exception. Is there a way to map the abstract classes during the runtime?
Like QuestionDTO -> Question, CriteriaDTO ->Criteria

I couldn't solve this problem with ModelMapper. Thus, I switched over to Dozer.
Dozer is a great tool for object mapping in Java. And it is really easy to use as well. You can define the corresponding mapping classes in a XML-file.

Here's a link to the documentation. http://dozer.sourceforge.net/documentation/mappings.html

My Solution with Spring
dozer-bean.xml

<bean class="org.dozer.spring.DozerBeanMapperFactoryBean" lazy-init="false">
        <property name="mappingFiles">
            <list>
                <value>META-INF/mapping/dozer-config.xml</value>
            </list>
        </property>
</bean>

dozer-config.xml

<mapping>
            <class-a>com.packagename.dto.QuestionDTO</class-a>
            <class-b>com.packagename.entities.core.Question</class-b>
</mapping>
<mapping>
        <class-a>com.packagename.dto.CriteriaDTO</class-a>
        <class-b>com.packagename.entities.core.Criteria</class-b>
</mapping>