title: Setting Default Value Strategy with Multiple Source Object in MapStruct
body: <p>I want to generate null checks on mapped properties of my source objects and set to a default value if indeed the source property is null.</p>
  <p>I have tried to use NullValuePropertyMappingStrategy.SET_TO_DEFAULT on @Mapper as well as on @Mapping targets but the generated code did not include the default setters..</p>
  <p>So basically what I am trying to achieve is:</p>
  <pre><code>@Mapper(componentModel = &quot;spring&quot;)
  public interface OperationDataMapper {
  
      OperationDTO from(Object 1 o1, Object2 o2);
  }
  </code></pre>
  <p>So that my generated code becomes:</p>
  <pre><code>@Component
  public class OperationDataMapperImpl implements OperationDataMapper {
  
      @Override 
      public OperationDTO from(Object 1 o1, Object2 o2) {
          if ( o1 == null &amp;&amp; o2 == null ) {
              return null;
          }
  
          OperationDTO operationDTO = new OperationDTO();
  
          if ( o1 != null ) {
              if(o1.getProp1() != null) {
                  operationDTO.setProp1( o1.getProp1() )
              } else {
                  operationDTO.setProp1( &quot;&quot; ) // if property is a string for example
              }
              .
              .
          }
      
          if ( o2 != null ) {
              if(o2.getProp2() != null) {
                  operationDTO.setProp2( o2.getProp2() )
              } else {
                  operationDTO.setProp2( &quot;&quot; ) // if property is a string for example
              }
              .
              .
          }
      
          return operationDTO;
      }
  }
  </code></pre>
  <p>I didn't write my example with the default value strategy like the documentation points out because I it did not work on my attempts to map the nested properties with null values.. Interesting enough, the NullValueCheckStrategy works without any problems but the NullValuePropertyMappingStrategy does not.</p>
  <p>I have also tried setting them using a @BeanMapping with no avail.</p>
  <p>If someone could please point me in the right direction I would appreciate it!</p>