No converter found capable of converting from type to type

Return ABDeadlineType from repository:

public interface ABDeadlineTypeRepository extends JpaRepository<ABDeadlineType, Long> {
    List<ABDeadlineType> findAllSummarizedBy();
}

and then convert to DeadlineType. Manually or use mapstruct.

Or call constructor from @Query annotation:

public interface DeadlineTypeRepository extends JpaRepository<ABDeadlineType, Long> {

    @Query("select new package.DeadlineType(a.id, a.code) from ABDeadlineType a ")
    List<DeadlineType> findAllSummarizedBy();
}

Or use @Projection:

@Projection(name = "deadline", types = { ABDeadlineType.class })
public interface DeadlineType {

    @Value("#{target.id}")
    String getId();

    @Value("#{target.code}")
    String getText();

}

Update:
Spring can work without @Projection annotation:

public interface DeadlineType {
    String getId();    
    String getText();
}