title: How to solve cloud Firestore plugin error in Flutter?
body: <p>My <code>Pubspec.yaml</code></p>
  <pre><code>  dev_dependencies:
    flutter_test:
      sdk: flutter
  
    carousel_pro: ^0.0.13
    firebase_auth: ^0.6.6
    google_sign_in: ^3.2.4
    cloud_firestore: ^0.8.2+3
    firebase_storage: ^1.0.4
    fluttertoast: ^2.2.3
    shared_preferences: ^0.4.3
    image_picker: ^0.4.10
    cached_network_image: ^0.5.1
    intl: ^0.15.7
    uuid:
    firebase_database:
    flutter_search_panel: ^1.0.1
    flutter_typeahead: ^1.4.0
  
  flutter:
  
    uses-material-design: true
    module:
      androidX: true 
  </code></pre>
  <p>But even though I am receiving the error:</p>
  <pre><code>C:\Users\RIDDHI\AppData\Local\Pub\Cache\hosted\pub.dartlang.org\cloud_firestore-0.8.2+3\android\src\main\java\io\flutter\plugins\firebase\cloudfirestore\CloudFirestorePlugin.java:8: error: package android.support.annotation does not exist
  import android.support.annotation.NonNull;
                                   ^
  C:\Users\RIDDHI\AppData\Local\Pub\Cache\hosted\pub.dartlang.org\cloud_firestore-0.8.2+3\android\src\main\java\io\flutter\plugins\firebase\cloudfirestore\CloudFirestorePlugin.java:9: error: package android.support.annotation does not exist
  import android.support.annotation.Nullable;
                                   ^
  C:\Users\RIDDHI\AppData\Local\Pub\Cache\hosted\pub.dartlang.org\cloud_firestore-0.8.2+3\android\src\main\java\io\flutter\plugins\firebase\cloudfirestore\CloudFirestorePlugin.java:253: error: cannot find symbol
            public void onFailure(@NonNull Exception e) {
                                   ^
    symbol: class NonNull
  C:\Users\RIDDHI\AppData\Local\Pub\Cache\hosted\pub.dartlang.org\cloud_firestore-0.8.2+3\android\src\main\java\io\flutter\plugins\firebase\cloudfirestore\CloudFirestorePlugin.java:274: error: cannot find symbol
                      public Void apply(@NonNull Transaction transaction)
                                         ^
    symbol: class NonNull
  C:\Users\RIDDHI\AppData\Local\Pub\Cache\hosted\pub.dartlang.org\cloud_firestore-0.8.2+3\android\src\main\java\io\flutter\plugins\firebase\cloudfirestore\CloudFirestorePlugin.java:272: error: cannot find symbol
                      @Nullable
                       ^
    symbol: class Nullable
  C:\Users\RIDDHI\AppData\Local\Pub\Cache\hosted\pub.dartlang.org\cloud_firestore-0.8.2+3\android\src\main\java\io\flutter\plugins\firebase\cloudfirestore\CloudFirestorePlugin.java:503: error: cannot find symbol
                      public void onFailure(@NonNull Exception e) {
                                             ^
    symbol: class NonNull
  C:\Users\RIDDHI\AppData\Local\Pub\Cache\hosted\pub.dartlang.org\cloud_firestore-0.8.2+3\android\src\main\java\io\flutter\plugins\firebase\cloudfirestore\CloudFirestorePlugin.java:558: error: cannot find symbol
                      public void onFailure(@NonNull Exception e) {
                                             ^
    symbol: class NonNull
  </code></pre>
  <p>Im trying to use code of <a href="https://github.com/Santos-Enoque/admin_side_flutter_ecommerce_app/tree/product_details" rel="nofollow noreferrer">https://github.com/Santos-Enoque/admin_side_flutter_ecommerce_app/tree/product_details</a>,
  Can someone please help me in understanding why this error is occurring and how to solve it?</p>