code: public static Specification<JpaTarget> hasTag(final Long tagId) {
  
          return (targetRoot, query, cb) -> {
              final SetJoin<JpaTarget, JpaTargetTag> tags = targetRoot.join(JpaTarget_.tags, JoinType.LEFT);
              return cb.equal(tags.get(JpaTargetTag_.id), tagId);
          };
      }
docs: {@link Specification} for retrieving {@link Target}s by tag.
  
  @param tagId
  the ID of the distribution set which must be assigned
  @return the {@link Target} {@link Specification}