docs: @Requires({
      "parent != null",
      "annotation != null"
    })
    @Ensures("result != null")
    @SuppressWarnings("unchecked")
    protected List<Long> getLineNumbers(Element parent,
                                        AnnotationMirror annotation) {
      if (JavaUtils.classExists("com.sun.source.util.Trees")) {
        try {
          return (List<Long>) Class
              .forName("com.google.java.contract.core.apt.JavacUtils")
              .getMethod("getLineNumbers", ProcessingEnvironment.class,
                         Element.class, AnnotationMirror.class)
              .invoke(null, utils.processingEnv, parent, annotation);
        } catch (Exception e) {
          return Collections.emptyList();
        }
      } else {
        return Collections.emptyList();
      }
    }