Laravel route link with parameter not work

in my route have optional parameter. when I click my link then its create problem.It looks like

http://localhost/my/public/admin/category/sub-create?2

But it will be

http://localhost/my/public/admin/category/sub-create/2

My route

     Route::get('sub-create/{cid?}',['as'=>'new_sub_category',
'uses'=>'CategoryController@SubCategoryCreate']);

My link

<a href="{{route('new_sub_category', $categoryID)}}"
     class="btn bg-navy btn-flat margin">
    <i class="fa fa-plus-square"></i> Add New Subcategory</a>

via Chebli Mohamed