The getter 'length' was called on null.

[mjhansen3]

I followed the documentation but I seem to be getting this issue.

I/flutter (26830): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (26830): The following NoSuchMethodError was thrown building UHungry(dirty):
I/flutter (26830): The getter 'length' was called on null.
I/flutter (26830): Receiver: null
I/flutter (26830): Tried calling: length
I/flutter (26830): 
I/flutter (26830): When the exception was thrown, this was the stack:
I/flutter (26830): #0      Object.noSuchMethod (dart:core-patch/object_patch.dart:50:5)
I/flutter (26830): #1      new AppTheme (package:theme_provider/src/data/app_theme.dart:84:24)
I/flutter (26830): #2      defaultMode (package:uHungry/main.dart:65:12)
I/flutter (26830): #3      UHungry.build (package:uHungry/main.dart:258:29)
I/flutter (26830): #4      StatelessElement.build (package:flutter/src/widgets/framework.dart:3886:28)
I/flutter (26830): #5      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3836:15)
I/flutter (26830): #6      Element.rebuild (package:flutter/src/widgets/framework.dart:3657:5)
I/flutter (26830): #7      ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3819:5)
I/flutter (26830): #8      ComponentElement.mount (package:flutter/src/widgets/framework.dart:3814:5)
I/flutter (26830): #9      Element.inflateWidget (package:flutter/src/widgets/framework.dart:3053:14)
I/flutter (26830): #10     Element.updateChild (package:flutter/src/widgets/framework.dart:2856:12)
I/flutter (26830): #11     RenderObjectToWidgetElement._rebuild (package:flutter/src/widgets/binding.dart:939:16)
I/flutter (26830): #12     RenderObjectToWidgetElement.mount (package:flutter/src/widgets/binding.dart:910:5)
I/flutter (26830): #13     RenderObjectToWidgetAdapter.attachToRenderTree.<anonymous closure> (package:flutter/src/widgets/binding.dart:856:17)
I/flutter (26830): #14     BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2295:19)
I/flutter (26830): #15     RenderObjectToWidgetAdapter.attachToRenderTree (package:flutter/src/widgets/binding.dart:855:13)
I/flutter (26830): #16     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding&WidgetsBinding.attachRootWidget (package:flutter/src/widgets/binding.dart:736:7)
I/flutter (26830): #17     runApp (package:flutter/src/widgets/binding.dart:786:7)
I/flutter (26830): #18     main.<anonymous closure> (package:uHungry/main.dart:58:9)
I/flutter (26830): #28     SystemChrome.setPreferredOrientations (package:flutter/src/services/system_chrome.dart)
I/flutter (26830): #39     OptionalMethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart)
I/flutter (26830): #50     MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart)
I/flutter (26830): (elided 43 frames from package dart:async and package dart:async-patch)
I/flutter (26830): ════════════════════════════════════════════════════════════════════════════════════════════════════

This occurs when I try to use my own custom AppTheme

AppTheme(
      id: "dark_mode",
      data: ThemeData(
          appBarTheme: AppBarTheme(
            color: Color(0xFF1E1E1E),
            elevation: 1.5,
          ),
          scaffoldBackgroundColor: Color(0xFF121212),
          backgroundColor: Color(0xFF1E1E1E),
          dialogBackgroundColor: Color(0xFF121212),
          bottomSheetTheme: BottomSheetThemeData(
              backgroundColor: Color(0xFF121212),
              elevation: 0,
              shape: RoundedRectangleBorder(
                  borderRadius: BorderRadius.only(
                    topLeft: Radius.circular(40),
                    topRight: Radius.circular(40),
                  )
              )
          ),
          textTheme: TextTheme(
            body1: TextStyle(
                color: Color(0xFFFFFFFF)
            ),
            body2: TextStyle(
                color: Color(0xFF8A8A8A)
            ),
            title: TextStyle(
                color: Color(0xFFFFFFFF)
            ),
            subtitle: TextStyle(
                color: Color(0xFF8A8A8A)
            ),
            caption: TextStyle(
                color: Color(0xFF8A8A8A)
            ),
            display1: TextStyle(
                color: Color(0xFFF05A22)
            ),
            display2: TextStyle(
                color: Color(0xFFFFFFFF)
            ),
            display3: TextStyle(
                color: Color(0xFF1E1E1E)
            ),
          ),
          cardColor: Color(0xFF1E1E1E),
          splashColor: Colors.transparent,
          highlightColor: Colors.transparent,
          inputDecorationTheme: InputDecorationTheme(
              filled: true,
              fillColor: Colors.transparent,
              enabledBorder: OutlineInputBorder(
                  borderSide: BorderSide(
                      color: Color(0xFF8A8A8A)
                  ),
                  borderRadius: BorderRadius.circular(30.0)
              ),
              focusedBorder: OutlineInputBorder(
                borderSide: BorderSide(
                    color: Color(0xFFF05A22)
                ),
                borderRadius: BorderRadius.circular(30.0),
              ),
              errorBorder: OutlineInputBorder(
                  borderSide: BorderSide(
                      color: Color(0xFFCE020D)
                  ),
                  borderRadius: BorderRadius.circular(30.0)
              ),
              focusedErrorBorder: OutlineInputBorder(
                  borderSide: BorderSide(
                      color: Color(0xFFCE020D)
                  ),
                  borderRadius: BorderRadius.circular(30.0)
              )
          )
      )
  )

[mjhansen3]

I was able to resolve it. Apparently, the issue occurred because I did not include the description property to my custom AppTheme. I don't understand why that should have happened, which is not required but including it fixed the issue for me.