Null check operator used on a null value when either only width or height gets provided

[BujusKrachus]

Usually you can only pass one of both (width/height) and the other one will be set accordingly. However only passing one throws a null check error. Providing both works just fine but is annoying to keep the aspect correct.

For example:

Expanded(
                    child: AnimatedDrawing.svg(
                      'image.svg',
                      width: 100, // note: only width provided
                      run: svgAnimation01,
                      duration: const Duration(seconds: 3),
                      lineAnimation: LineAnimation.oneByOne,
                      animationCurve: Curves.linear,
                      onFinish: () => setState(() {
                        //run = false;
                      }),
                    ),
                  ),

will throw:

======== Exception caught by widgets library =======================================================
The following _TypeError was thrown building AnimatedDrawing(dirty, dependencies: [MediaQuery], state: AnimatedDrawingWithTickerState#2b228(ticker inactive)):
Null check operator used on a null value

The relevant error-causing widget was: 
  AnimatedDrawing AnimatedDrawing:file:///C:/Users/<user>/<path_to_file>.dart:<line>
When the exception was thrown, this was the stack: 
#0      AbstractAnimatedDrawingState.getCustomDimensions (package:drawing_animation/src/abstract_drawing_state.dart:214:22)
#1      AbstractAnimatedDrawingState.preparePathPainterBuilder (package:drawing_animation/src/abstract_drawing_state.dart:164:33)
#2      AbstractAnimatedDrawingState.buildForegroundPainter (package:drawing_animation/src/abstract_drawing_state.dart:149:19)
#3      AbstractAnimatedDrawingState.createCustomPaint (package:drawing_animation/src/abstract_drawing_state.dart:224:28)
#4      AnimatedDrawingWithTickerState.build (package:drawing_animation/src/drawing_state_with_ticker.dart:55:12)
#5      StatefulElement.build (package:flutter/src/widgets/framework.dart:5592:27)
#6      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:5480:15)
#7      StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:5643:11)
#8      Element.rebuild (package:flutter/src/widgets/framework.dart:5196:7)
#9      BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2904:19)
#10     WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:989:21)
#11     RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:448:5)
#12     SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1386:15)
#13     SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:1311:9)
#14     SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:1169:5)
#15     _invoke (dart:ui/hooks.dart:312:13)
#16     PlatformDispatcher._drawFrame (dart:ui/platform_dispatcher.dart:399:5)
#17     _drawFrame (dart:ui/hooks.dart:283:31)
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