safeInvoke = function safeInvoke(fn) {
  if (typeof fn === "function") {
    for (var _len = arguments.length, args = new Array(_len > 1 ? _len - 1 : 0), _key = 1; _key < _len; _key++) {
      args[_key - 1] = arguments[_key];
    }

    return fn.apply(void 0, args);
  }
}
Takes a maybe-undefined function and arbitrary args and invokes the function
only if it is defined.