Confused on a LINQ where clause

public ViewResult List(string category, int page = 1) 
{
    ProductsListViewModel viewModel = new ProductsListViewModel
    {
        Products = repository.Products
            .Where(p => category == null || p.Category == category)
            ...........

The line : .Where(p => category == null || p.Category == category) is a little confusing to me. The logic is : "If category is null, then only select the selected category". This is from a book, but is this the best way to write this? It's saying the category can be "null OR an category value". So if category contains a value, it will use that value to select the items and not null (null selects all items). I wrote this which is kind of useless but works and makes its clearer :

.Where(p => category == null ? category == null :
                               p.Category == category)

Am I getting this logic right?