title: Flutter Error: Method 'addPostFrameCallback' cannot be called on 'WidgetsBinding?' because it is potentially null
body: <p>Whenever I try to run flutter app, I am getting this error.</p>
  <pre><code>../flutter/.pub-cache/hosted/pub.dartlang.org/percent_indicator-4.2.1/lib/linear_percent_indicator.dart:162:5: Warning: The class 'WidgetsBinding' cannot be null.
  Try replacing '?.' with '.'
      WidgetsBinding?.instance.addPostFrameCallback((_) {
      ^^^^^^^^^^^^^^
  ../flutter/.pub-cache/hosted/pub.dartlang.org/percent_indicator-4.2.1/lib/linear_percent_indicator.dart:162:30: Error: Method 'addPostFrameCallback' cannot be called on 'WidgetsBinding?' because it is potentially null.
   - 'WidgetsBinding' is from 'package:flutter/src/widgets/binding.dart' ('../flutter/packages/flutter/lib/src/widgets/binding.dart').
  Try calling using ?. instead.
      WidgetsBinding?.instance.addPostFrameCallback((_) {
                               ^^^^^^^^^^^^^^^^^^^^
  
  
  FAILURE: Build failed with an exception.
  
  * Where:
  Script '/home/user/Downloads/flutter/packages/flutter_tools/gradle/flutter.gradle' line: 1102
  
  * What went wrong:
  Execution failed for task ':app:compileFlutterBuildDebug'.
  &gt; Process 'command '/home/user/Downloads/flutter/bin/flutter'' finished with non-zero exit value 1
  
  * Try:
  Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
  
  * Get more help at https://help.gradle.org
  
  BUILD FAILED in 22s
  Running Gradle task 'assembleDebug'...                             22.8s
  Exception: Gradle task assembleDebug failed with exit code 1
  
  </code></pre>
  <p>Here, is my Flutter doctor output</p>
  <pre><code>[✓] Flutter (Channel stable, 2.10.3, on Ubuntu 20.04.4 LTS 5.13.0-41-generic, locale en_IN)
      • Flutter version 2.10.3 at /home/user/Downloads/flutter
      • Upstream repository https://github.com/flutter/flutter.git
      • Framework revision 7e9793dee1 (3 months ago), 2022-03-02 11:23:12 -0600
      • Engine revision bd539267b4
      • Dart version 2.16.1
      • DevTools version 2.9.2
  
  [✓] Android toolchain - develop for Android devices (Android SDK version 32.1.0-rc1)
      • Android SDK at /home/user/Android/Sdk
      • Platform android-32, build-tools 32.1.0-rc1
      • Java binary at: /opt/android-studio-2021.1.1/android-studio/jre/bin/java
      • Java version OpenJDK Runtime Environment (build 11.0.11+0-b60-7590822)
      • All Android licenses accepted.
  
  [✓] Chrome - develop for the web
      • Chrome at google-chrome
  
  [✓] Android Studio (version 2021.1)
      • Android Studio at /opt/android-studio-2021.1.1/android-studio
      • Flutter plugin version 66.0.1
      • Dart plugin version 211.7811
      • Java version OpenJDK Runtime Environment (build 11.0.11+0-b60-7590822)
  
  [✓] Android Studio
      • Android Studio at /opt/android-studio
      • Flutter plugin can be installed from:
         https://plugins.jetbrains.com/plugin/9212-flutter
      • Dart plugin can be installed from:
         https://plugins.jetbrains.com/plugin/6351-dart
      • Java version OpenJDK Runtime Environment (build 11.0.11+0-b60-7590822)
  
  [✓] Connected device (2 available)
      • sdk gphone64 x86 64 (mobile) • emulator-5554 • android-x64    • Android 12 (API 31) (emulator)
      • Chrome (web)                 • chrome        • web-javascript • Google Chrome 99.0.4844.82
  
  [✓] HTTP Host Availability
      • All required HTTP hosts are available
  
  • No issues found!
  
  </code></pre>
  <p>I have tried following things already</p>
  <ol>
  <li>Invalidate and restart android-studio</li>
  <li>Deleted .gradle folder and try building again</li>
  <li><code>flutter clean</code> and then 'flutter pub get<code>, </code>flutter pub cache repair`
  <ul>
  <li>also deleted build folder and pubspec.lock file</li>
  </ul>
  </li>
  </ol>
  <p><strong>But nothing, worked</strong></p>
  <p>Also, here is my Gradle files</p>
  <p>android/app/build.gradle</p>
  <pre><code>def localProperties = new Properties()
  def localPropertiesFile = rootProject.file('local.properties')
  if (localPropertiesFile.exists()) {
      localPropertiesFile.withReader('UTF-8') { reader -&gt;
          localProperties.load(reader)
      }
  }
  
  def flutterRoot = localProperties.getProperty('flutter.sdk')
  if (flutterRoot == null) {
      throw new GradleException(&quot;Flutter SDK not found. Define location with flutter.sdk in the local.properties file.&quot;)
  }
  
  def flutterVersionCode = localProperties.getProperty('flutter.versionCode')
  if (flutterVersionCode == null) {
      flutterVersionCode = '1'
  }
  
  def flutterVersionName = localProperties.getProperty('flutter.versionName')
  if (flutterVersionName == null) {
      flutterVersionName = '1.0'
  }
  
  apply plugin: 'com.android.application'
  apply plugin: 'kotlin-android'
  apply from: &quot;$flutterRoot/packages/flutter_tools/gradle/flutter.gradle&quot;
  apply plugin: 'com.google.gms.google-services'
  android {
      compileSdkVersion flutter.compileSdkVersion
  
      compileOptions {
          sourceCompatibility JavaVersion.VERSION_1_8
          targetCompatibility JavaVersion.VERSION_1_8
      }
  
      kotlinOptions {
          jvmTarget = '1.8'
      }
  
      sourceSets {
          main.java.srcDirs += 'src/main/kotlin'
      }
      splits {
          abi {
              enable true
              reset()
              include 'x86', 'armeabi-v7a'
              universalApk true
          }
      }
      defaultConfig {
          // TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).
          applicationId &quot;com.example.app.example&quot;
          minSdkVersion 19
          targetSdkVersion flutter.targetSdkVersion
          versionCode flutterVersionCode.toInteger()
          versionName flutterVersionName
          multiDexEnabled = true
      }
      // signingConfigs {
      //     debug {
      //         if (debugKeystorePropertiesFile.exists()) {
      //             keyAlias debugKeystoreProperties['keyAlias']
      //             keyPassword debugKeystoreProperties['keyPassword']
      //             storeFile file(debugKeystoreProperties['storeFile'])
      //             storePassword debugKeystoreProperties['storePassword']
      //         }
      //     }
      // }
      buildTypes {
          release {
  //            if (keystorePropertiesFile.exists()) {
  //                signingConfig signingConfigs.release
  //                println &quot;Signing with key.properties&quot;
  //            } else {
                  signingConfig signingConfigs.debug
                  println &quot;Signing with debug keys&quot;
  //            }
          }
      }
  }
  
  flutter {
      source '../..'
  }
  
  dependencies {
      implementation &quot;org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version&quot;
      implementation platform('com.google.firebase:firebase-bom:29.2.1')
      implementation 'com.google.firebase:firebase-auth-ktx'
      implementation 'com.google.android.gms:play-services-safetynet:18.0.1'
      implementation 'com.google.firebase:firebase-appcheck-safetynet:16.0.0-beta05'
  
      implementation &quot;androidx.browser:browser:1.3.0&quot;
  }
  
  </code></pre>
  <p>android/build.gradle</p>
  <pre><code>buildscript {
      ext.kotlin_version = '1.6.10'
      repositories {
          google()
          mavenCentral()
      }
  
      dependencies {
          classpath 'com.android.tools.build:gradle:4.1.0'
          classpath &quot;org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version&quot;
          classpath 'com.google.gms:google-services:4.3.10'
      }
  }
  
  allprojects {
      repositories {
          google()
          mavenCentral()
      }
  }
  
  rootProject.buildDir = '../build'
  subprojects {
      project.buildDir = &quot;${rootProject.buildDir}/${project.name}&quot;
  }
  subprojects {
      project.evaluationDependsOn(':app')
  }
  
  task clean(type: Delete) {
      delete rootProject.buildDir
  }
  
  </code></pre>
  <ul>
  <li>I do have added <code>android.useAndroidX</code> and <code>android.enableJetifier</code> to true</li>
  <li>Also added <code>android:exported=&quot;true&quot;</code> in androidmanifest.xml</li>
  </ul>