can't find method using null - dart

Question

Some method is initializing with null. There is no warnings or errors anywhere. And I triple checked the code that I thought had a mistake but I could not find anything.
Console Log Snippet:
I/flutter (21233): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY
╞═══════════════════════════════════════════════════════════
I/flutter (21233): The following NoSuchMethodError was thrown building Builder:
I/flutter (21233): The method '[]' was called on null.
I/flutter (21233): Receiver: null
I/flutter (21233): Tried calling:
I/flutter (21233): When the exception was thrown, this was the stack:
I/flutter (21233): #0
Object.noSuchMethod (dart:core/runtime/libobject_patch.dart:50:5)
I/flutter (21233): #1
ButtonsLists.foodList (package:customer/lists.dart:35:71)
I/flutter (21233): #2
ButtonsLists.foodList (package:customer/lists.dart:33:24)
=========================================================================
https://gist.github.com/Norman518/17be934d342b7523e80c7abc2e40aced
final List<MainButtons> buttonList = [
MainButtons(Icons.domain, 'Class Supplies', Page(suppliesList)),
MainButtons(Icons.local_dining, 'Food and Snacks', Page(foodList)),
MainButtons(Icons.hot_tub, 'Personal Supplies', Page(toiletriesList)),
MainButtons(Icons.local_cafe, 'Drinks', Page(drinksList))
];
MainButtons(this.image, this.name, this.onTap);
final IconData image;
final String name;
final Route onTap;
.
.
.
onTap: () {
Navigator.of(context).push(onTap);
},
=========================================================================
I expect four inkwell buttons to be displayed.
=========================================================================
Did the change, here is the console output
I/flutter ( 4037): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter ( 4037): The following CyclicInitializationError was thrown building Builder:
I/flutter ( 4037): Reading static variable 'suppliesList' during its initialization
I/flutter ( 4037): When the exception was thrown, this was the stack:
I/flutter ( 4037): #0 ButtonsLists.suppliesList (package:customer/lists.dart:26:24)
I/flutter ( 4037): #1 new ButtonsLists (package:customer/lists.dart:55:54)
I/flutter ( 4037): #2 new BuyItem (package:customer/buyItem.dart:66:35)
I/flutter ( 4037): #3 ButtonsLists.buyItemList (package:customer/lists.dart:8:5)
I/flutter ( 4037): #4 ButtonsLists.buyItemList (package:customer/lists.dart:7:23)

Answer 1

I think the problem lies here
BrowsePage(this.buttonList);
final List<Widget> buttonList;
instead try this way
final List<Widget> buttonList;
BrowsePage(this.buttonList);

Answer 2

Don't put the list in the login page and buyitem, put it in the browsepage.