I use frozenColumns and get some error in grid

[wow-prime]

My code in grid like below:

protected getSlickOptions() {
var opt = super.getSlickOptions();
opt.frozenColumns = 7;
opt.layoutEngine = new FrozenLayout();
return opt;
}

And I get some error below:

My serenity version is 6.6.0.

But it is OK, when i use the same code in serenity version 8.7.0.
How can i modify code in version 6.6.0. .