In the case of undefined `value`, this preserves the old behavior of omitting the corresponding attribute from resulting checkboxes, which is assumed "true" by the event handlers: https://github.com/gibson042/qunit/compare/c7c466f11a1b5ebbf7e1eacf8ec31ca1d312d050%5E...c621f60ee458d99ad076e6e2953f12b63cdc2867#diff-7eb52b366866677666470e019283c8eaL665