Null check operator used on a null value

[Skyost]

Hey,
I've successfully implemented flutter_math in a RichText widget (see znjameswu/flutter_math#29 (comment)). But I still have some problems :

======== Exception caught by rendering library =====================================================
The following _CastError was thrown during performLayout():
Null check operator used on a null value

The relevant error-causing widget was: 
  RichText file:///D:/Hugo/Projets/Flutter/bacomathiques/lib/pages/html/widgets/math_widget.dart:41:12
When the exception was thrown, this was the stack: 
#0      MultiscriptsLayoutDelegate.performHorizontalIntrinsicLayout (package:flutter_math_fork/src/render/layout/multiscripts.dart:136:53)
#1      IntrinsicLayoutDelegate.performLayout (package:flutter_math_fork/src/render/layout/custom_layout.dart:266:19)
#2      RenderCustomLayout.performLayout (package:flutter_math_fork/src/render/layout/custom_layout.dart:198:27)
#3      RenderObject.layout (package:flutter/src/rendering/object.dart:1784:7)
#4      RenderLine.performLayout (package:flutter_math_fork/src/render/layout/line.dart:332:15)
...
The following RenderObject was being processed when the exception was fired: RenderCustomLayout<_ScriptPos>#19c04 relayoutBoundary=up35 NEEDS-LAYOUT NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE
...  parentData: offset=Offset(0.0, 0.0); canBreakBefore = false; customSize = false; trailingMargin = 4.444444444444445; alignerOrSpacer = false (can use size)
...  constraints: BoxConstraints(unconstrained)
...  size: MISSING
RenderObject: RenderCustomLayout<_ScriptPos>#19c04 relayoutBoundary=up35 NEEDS-LAYOUT NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE
  parentData: offset=Offset(0.0, 0.0); canBreakBefore = false; customSize = false; trailingMargin = 4.444444444444445; alignerOrSpacer = false (can use size)
  constraints: BoxConstraints(unconstrained)
  size: MISSING
====================================================================================================

The problem seems to be the following line (in src/render/layout/multiscripts.dart) :

[Skyost]

It seems it was just a problem with line breaking on \displaystyle{\int_1^4 2x + 1 \, \mathrm{d}x = \left[ x(x+1) \right]_1^4 = 4(4+1) - 1(1+1) = 20-2 = 18}. I have removed the displaystyle and it works.

I leave this issue opened in case you're interested but feel free to close it 😉