Issue 1:
Steps to Reproduce

return new Scaffold(
appBar: new AppBar(
title: new Text('Enter text to read'),
),
body: new Center(
child: new TextField(
maxLines: null,
decoration: new InputDecoration(
hintText: 'Enter some text for paced reading',
),
onChanged: _action,
onSubmitted: (String str) {
Navigator.of(context).push(new MaterialPageRoute<Null>(
builder: (_) => new MyReadPage(text: str)));
}),
));

Though, it seems to happen somewhat sporadically. First it happened on first load, later it happened upon deleting some characters.

Logs

I/flutter (28170): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (28170): The following NoSuchMethodError was thrown building _TextSelectionHandleOverlay(dirty, state:
I/flutter (28170): _TextSelectionHandleOverlayState#8b639):
I/flutter (28170): The method 'toDouble' was called on null.
I/flutter (28170): Receiver: null
I/flutter (28170): Tried calling: toDouble()
I/flutter (28170):
I/flutter (28170): When the exception was thrown, this was the stack:
I/flutter (28170): #0 Object.noSuchMethod (dart:core-patch/dart:core/object_patch.dart:46)
I/flutter (28170): #1 double./ (dart:core-patch/dart:core/double.dart:41)
I/flutter (28170): #2 _TextSelectionHandleOverlayState.build (package:flutter/src/widgets/text_selection.dart:512:49)
I/flutter (28170): #3 StatefulElement.build (package:flutter/src/widgets/framework.dart:3640:27)
I/flutter (28170): #4 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3550:15)
I/flutter (28170): #5 Element.rebuild (package:flutter/src/widgets/framework.dart:3451:5)
I/flutter (28170): #6 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3530:5)
I/flutter (28170): #7 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3668:22)
I/flutter (28170): #8 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3525:5)
I/flutter (28170): #9 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2890:14)
I/flutter (28170): #10 Element.updateChild (package:flutter/src/widgets/framework.dart:2693:12)
I/flutter (28170): #11 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4533:14)
I/flutter (28170): #12 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2890:14)
I/flutter (28170): #13 Element.updateChild (package:flutter/src/widgets/framework.dart:2693:12)
I/flutter (28170): #14 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3562:16)
I/flutter (28170): #15 Element.rebuild (package:flutter/src/widgets/framework.dart:3451:5)
I/flutter (28170): #16 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3530:5)
I/flutter (28170): #17 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3668:22)
I/flutter (28170): #18 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3525:5)
I/flutter (28170): #19 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2890:14)
I/flutter (28170): #20 Element.updateChild (package:flutter/src/widgets/framework.dart:2693:12)
I/flutter (28170): #21 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3562:16)
I/flutter (28170): #22 Element.rebuild (package:flutter/src/widgets/framework.dart:3451:5)
I/flutter (28170): #23 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3530:5)
I/flutter (28170): #24 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3668:22)
I/flutter (28170): #25 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3525:5)
I/flutter (28170): #26 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2890:14)
I/flutter (28170): #27 Element.updateChild (package:flutter/src/widgets/framework.dart:2693:12)
I/flutter (28170): #28 RenderObjectElement.updateChildren (package:flutter/src/widgets/framework.dart:4325:32)
I/flutter (28170): #29 MultiChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4648:17)
I/flutter (28170): #30 Element.updateChild (package:flutter/src/widgets/framework.dart:2682:15)
I/flutter (28170): #31 _TheatreElement.update (package:flutter/src/widgets/overlay.dart:507:16)
I/flutter (28170): #32 Element.updateChild (package:flutter/src/widgets/framework.dart:2682:15)
I/flutter (28170): #33 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3562:16)
I/flutter (28170): #34 Element.rebuild (package:flutter/src/widgets/framework.dart:3451:5)
I/flutter (28170): #35 BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2251:33)
I/flutter (28170): #36 BindingBase&SchedulerBinding&GestureBinding&ServicesBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:580:20)
I/flutter (28170): #37 BindingBase&SchedulerBinding&GestureBinding&ServicesBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:200:5)
I/flutter (28170): #38 BindingBase&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:713:15)
I/flutter (28170): #39 BindingBase&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:649:9)
I/flutter (28170): #40 _invoke (file:///b/build/slave/Linux_Engine/build/src/flutter/lib/ui/hooks.dart:91)
I/flutter (28170): #41 _drawFrame (file:///b/build/slave/Linux_Engine/build/src/flutter/lib/ui/hooks.dart:80)
I/flutter (28170): ════════════════════════════════════════════════════════════════════════════════════════════════════

analyze reported no issues

Flutter Doctor

[✓] Flutter (on Linux, locale en_US.UTF-8, channel alpha)
• Flutter at /home/mfairhurst/dart/flutter
• Framework revision e8aa40eddd (4 weeks ago), 2017-10-17 15:42:40 -0700
• Engine revision 7c4142808c
• Tools Dart version 1.25.0-dev.11.0

[✗] Android toolchain - develop for Android devices
✗ Unable to locate Android SDK.
Install Android Studio from: https://developer.android.com/studio/index.html
On first launch it will assist you in installing the Android SDK components.
(or visit https://flutter.io/setup/#android-setup for detailed instructions).
If Android SDK has been installed to a custom location, set $ANDROID_HOME to that location.

[✗] Android Studio (not installed)
• Android Studio not found; download from https://developer.android.com/studio/index.html
(or visit https://flutter.io/setup/#android-setup for detailed instructions).

[-] IntelliJ IDEA Ultimate Edition (version 2016.2)
✗ Flutter plugin not installed; this adds Flutter specific functionality.
• Dart plugin version 162.2485
• For information about installing plugins, see
https://flutter.io/intellij-setup/#installing-the-plugins
✗ This install is older than the minimum recommended version of 2017.1.0.

[-] IntelliJ IDEA Ultimate Edition (version 2017.2)
✗ Flutter plugin not installed; this adds Flutter specific functionality.
• Dart plugin version 172.2791
• For information about installing plugins, see
https://flutter.io/intellij-setup/#installing-the-plugins

[-] IntelliJ IDEA Ultimate Edition (version 2016.3)
✗ Flutter plugin not installed; this adds Flutter specific functionality.
• Dart plugin version 163.8651
• For information about installing plugins, see
https://flutter.io/intellij-setup/#installing-the-plugins
✗ This install is older than the minimum recommended version of 2017.1.0.

Issue 2:
Longpress on TextField with maxLines set to null, an exception occurs.

If maxLines is a number, no exception.

The following NoSuchMethodError was thrown building _TextSelectionHandleOverlay(dirty, state:
_TextSelectionHandleOverlayState#c8639):
The method 'toDouble' was called on null.
Receiver: null
Tried calling: toDouble()
When the exception was thrown, this was the stack:
#0 Object._noSuchMethod (dart:core-patch/object_patch.dart:42)
#1 Object.noSuchMethod (dart:core-patch/object_patch.dart:46)
#2 double./ (dart:core-patch/double.dart:39)
#3 _TextSelectionHandleOverlayState.build (package:flutter/src/widgets/text_selection.dart:512:49)
#4 StatefulElement.build (package:flutter/src/widgets/framework.dart:3624:27)
#5 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3534:15)
#6 Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#7 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3514:5)
#8 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3652:22)
#9 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3509:5)
#10 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2882:14)
#11 Element.updateChild (package:flutter/src/widgets/framework.dart:2685:12)
#12 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4516:14)
#13 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2882:14)
#14 Element.updateChild (package:flutter/src/widgets/framework.dart:2685:12)
#15 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#16 Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#17 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3514:5)
#18 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3652:22)
#19 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3509:5)
#20 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2882:14)
#21 Element.updateChild (package:flutter/src/widgets/framework.dart:2685:12)
#22 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#23 Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#24 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3514:5)
#25 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3652:22)
#26 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3509:5)
#27 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2882:14)
#28 Element.updateChild (package:flutter/src/widgets/framework.dart:2685:12)
#29 RenderObjectElement.updateChildren (package:flutter/src/widgets/framework.dart:4308:32)
#30 MultiChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4631:17)
#31 Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#32 _TheatreElement.update (package:flutter/src/widgets/overlay.dart:507:16)
#33 Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#34 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#35 Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#36 BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2260:33)
#37 BindingBase&SchedulerBinding&GestureBinding&ServicesBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:503:20)
#38 BindingBase&SchedulerBinding&GestureBinding&ServicesBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:189:5)
#39 BindingBase&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:695:15)
#40 BindingBase&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:643:9)
#41 _invoke (file:///b/build/slave/Mac_Engine/build/src/flutter/lib/ui/hooks.dart:86)
#42 _drawFrame (file:///b/build/slave/Mac_Engine/build/src/flutter/lib/ui/hooks.dart:75)

Simple reproduction:

void main() {
runApp(new MaterialApp(
home: new Scaffold(
body: new Container(
child: new TextField(maxLines: null),
constraints: const BoxConstraints.expand(),
),
),
));
}

Flutter doctor:

[✓] Flutter (on Mac OS X 10.12.6 16G29, locale ja-JP, channel master)
• Flutter at /Applications/flutter
• Framework revision 3b76e7e258 (28 hours ago), 2017-08-08 15:46:47 -0700
• Engine revision f0d440bec3
• Tools Dart version 1.25.0-dev.7.0

[✓] Android toolchain - develop for Android devices (Android SDK 25.0.3)
• Android SDK at /Users/najeira/Library/Android/sdk
• Platform android-25, build-tools 25.0.3
• ANDROID_HOME = /Users/najeira/Library/Android/sdk
• Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
• Java version OpenJDK Runtime Environment (build 1.8.0_112-release-b06)

[✓] iOS toolchain - develop for iOS devices (Xcode 8.3.3)
• Xcode at /Applications/Xcode.app/Contents/Developer
• Xcode 8.3.3, Build version 8E3004b
• ios-deploy 1.9.1
• CocoaPods version 1.2.1

[✓] Android Studio (version 2.3)
• Android Studio at /Applications/Android Studio.app/Contents
• Java version OpenJDK Runtime Environment (build 1.8.0_112-release-b06)

[✓] IntelliJ IDEA Ultimate Edition (version 2017.2.1)
• Flutter plugin version 16.0
• Dart plugin version 172.3544.34