test_that("Test NULL values", {
  namedlist <- structure(list(), .Names = character(0));
  x <- NULL
  y <- list(a=NULL, b=NA)
  z <- list(a=1, b=character(0))

  expect_true(validate(toJSON(x)))
  expect_equal(fromJSON(toJSON(x)), namedlist);
  expect_equal(toJSON(x), "{}");
  expect_equal(toJSON(x, null="list"), "{}");

  expect_true(validate(toJSON(y)))
  expect_equal(toJSON(y, null="list"), "{\"a\":{},\"b\":[null]}");
  expect_equal(toJSON(y, null="null"), "{\"a\":null,\"b\":[null]}");
  expect_equal(fromJSON(toJSON(y, null="null")), y);
  expect_equal(fromJSON(toJSON(y, null="list")), list(a=namedlist, b=NA));

  expect_true(validate(toJSON(z)))
  expect_equal(toJSON(z), "{\"a\":[1],\"b\":[]}");
  expect_equal(fromJSON(toJSON(z)), list(a=1, b=list()));
});