After added cloud_firestore: ^0.14.3+1 (I am not quite sure if it is the only reason), run on Android emulator, failed, it saids Execution failed for task ':app:mergeDexDebug'.

TahaTesser gives a hint:

You need to enable multidex

lordvidex provided a solution:
Go to android/app/build.gradle, add the following lines of codes:

dependencies {
  implementation 'com.android.support:multidex:1.0.3' //enter the latest version
}
android {
    defaultConfig {
        multiDexEnabled true
    }
}

Run again, succeed.

Hope this helps!
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