Play Store signing config with gradle kts fails in debug mode

[julien4215]

Page URL

https://docs.flutter.dev/deployment/android#configure-signing-in-gradle

Page source

https://github.com/flutter/website/blob/main/src/content/deployment/android.md#configure-signing-in-gradle

Describe the problem

The website will offer to use the signing config below for release mode but if you don't have the key.properties file it will prevent the app from building in debug mode.

android {
    ...
    signingConfigs {
        create("release") {
            keyAlias = keystoreProperties["keyAlias"] as String
            keyPassword = keystoreProperties["keyPassword"] as String
            storeFile = keystoreProperties["storeFile"]?.let { file(it) }
            storePassword = keystoreProperties["storePassword"] as String
        }
    }
    buildTypes {
        release {
            signingConfig = signingConfigs.getByName("release")
        }
    }
...
}

The build fails with this error.

FAILURE: Build failed with an exception.

* Where:
Build file '/path/to/project/android/app/build.gradle.kts' line: 44

* What went wrong:
null cannot be cast to non-null type kotlin.String

Expected fix

Cast to String? instead of String would solve the error but I think ideally the file key.properties should only be read in release mode.

Additional context

To reproduce

1. create a Flutter project
2. Replace build.gradle.kts with the one below
3. Run flutter build apk --debug

import java.util.Properties
import java.io.FileInputStream

plugins {
    id("com.android.application")
    id("kotlin-android")
    // The Flutter Gradle Plugin must be applied after the Android and Kotlin Gradle plugins.
    id("dev.flutter.flutter-gradle-plugin")
}

val keystoreProperties = Properties()
val keystorePropertiesFile = rootProject.file("key.properties")
if (keystorePropertiesFile.exists()) {
    keystoreProperties.load(FileInputStream(keystorePropertiesFile))
}

android {
    namespace = "com.example.test"
    compileSdk = flutter.compileSdkVersion
    ndkVersion = flutter.ndkVersion

    compileOptions {
        sourceCompatibility = JavaVersion.VERSION_11
        targetCompatibility = JavaVersion.VERSION_11
    }

    kotlinOptions {
        jvmTarget = JavaVersion.VERSION_11.toString()
    }

    defaultConfig {
        // TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).
        applicationId = "com.example.test"
        // You can update the following values to match your application needs.
        // For more information, see: https://flutter.dev/to/review-gradle-config.
        minSdk = flutter.minSdkVersion
        targetSdk = flutter.targetSdkVersion
        versionCode = flutter.versionCode
        versionName = flutter.versionName
    }

    signingConfigs {
        create("release") {
            keyAlias = keystoreProperties["keyAlias"] as String
            keyPassword = keystoreProperties["keyPassword"] as String
            storeFile = keystoreProperties["storeFile"]?.let { file(it) }
            storePassword = keystoreProperties["storePassword"] as String
        }
    }

    buildTypes {
        release {
            signingConfig = signingConfigs.getByName("release")
        }
    }
}

flutter {
    source = "../.."
}