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