(Dart) How can I create a sub list of only certain items in the first list containing a string?

(Dart) How can I create a sub list of only certain items in the first list containing a string?

Problem Description:

Here is my are my List Items:

static List<Category> getMockedCategories(){
  return[
    Category(
      name: "Ascent",
      imgName: "AscentLoading",
      subCategories: [
        SubCategory(
          name: "ascent",
            imgName: "ascent_a_sova_frontgen"
        )
      ]
    ),
    Category(
        name: "Breeze",
        imgName: "BreezeLoading",
        subCategories: [
        ]
    ),

The category class:

class Category{
  String name;
  String imgName;
  List<Category>? subCategories;

  Category(
    {
      required this.name,
      required this.imgName,
      this.subCategories
    }
    );
}

The Subcategory Class:

class SubCategory extends Category {

    SubCategory({
      required String name,
      required String imgName,
    }): super(
      name: name,
      imgName: imgName
    );
}

When trying to create a ListView of my images with only a certain name in their imgName I am running into this error:
======== Exception caught by widgets library =======================================================
The following RangeError was thrown building SelectedCategoryPage(dirty):
RangeError (index): Invalid value: Only valid value is 0: 1

If comment out the catList section and just have pointer pointing at the selectedCategory.subCategories it works fine. I can’t see why its not working for catList. Any help is appreciated.

Here is the code for the page running into the issue:

var catList = [];
for(int j = 0; j <= selectedCategory.subCategories!.length; j++){
  if( selectedCategory.subCategories![j].imgName.contains(globals.agentSelected) ){
    catList.add(selectedCategory.subCategories![j]);
  }
}
var pointer = selectedCategory.subCategories;
if(catList[0] != null){
  pointer = catList.cast<Category>();
}

Tried creating another List of Categories to pass to listview builder but am receving an error on it:
======== Exception caught by widgets library =======================================================
The following RangeError was thrown building SelectedCategoryPage(dirty):
RangeError (index): Invalid value: Only valid value is 0: 1

Solution – 1

Could you try changing:
j <= selectedCategory.subCategories!.length to j < selectedCategory.subCategories!.length

j cannot have a position equals to the length of subCategories.

You can also do this:

var pointer = selectedCategory.subCategories;
if(catList.isNotEmpty){
  pointer = catList.cast<Category>(); //Try using a for loop here if this statement gives you an error
}