Firebase dependency in Android Library: Cannot invoke method get() on null object

Question

I'm experiencing a build issue when adding a firebase dependency to a android library.

My setup is as follows

/settings.gradle

include ':module-lib'
include ':module-app'

/build.gradle

buildscript {
  dependencies {
    classpath 'com.android.tools.build:gradle:3.1.2'
    classpath 'com.google.gms:google-services:4.0.0'
  } 
}

/module-lib/build.gradle

apply plugin: 'com.android.library'
android {
   ...
}
dependencies{
  api "com.google.firebase:firebase-config:16.0.0"  
}

/module-app/build.gradle

apply plugin: 'com.android.application'
android {
   ...
}
dependencies {
  implementation project(':module-lib') 
}
apply plugin: 'com.google.gms.google-services'

Short log:

$ ./gradlew clean build

Starting a Gradle Daemon, 1 busy and 2 stopped Daemons could not be reused, use --status for details

Parallel execution is an incubating feature.

> Configure project :module-app
Detected alwaysUpdateBuildId set to false while obfuscation is enabled. This may result in obfuscated stack traces in Crashlytics.
registerResGeneratingTask is deprecated, use registerGeneratedResFolders(FileCollection)
registerResGeneratingTask is deprecated, use registerGeneratedResFolders(FileCollection)
registerResGeneratingTask is deprecated, use registerGeneratedResFolders(FileCollection)
registerResGeneratingTask is deprecated, use registerGeneratedResFolders(FileCollection)

> Task :module-lib:compileDebugAidl FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Failed to notify dependency resolution listener.
> Cannot invoke method get() on null object
> Cannot invoke method get() on null object

* 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 18s
13 actionable tasks: 8 executed, 5 from cache

You can find the full stacktrace of the original error in this pastebin

The funny thing is that module-lib only contains a placeholder, empty and useless class. If I removed the firebase dependency from module-lib and move it to module-app, the build works fine.

I'm not using Android Studio, so this is a purely Gradle and/or plugin and/or dependencies issue.

Also note that

./gradlew clean       // Always succeds 
./gradlew build       // Sometimes works with above error 
./gradlew clean build // Always fails with above error

This also happens with any firebase-* dependency included in a module that applies the library plugin com.android.library.

More environment info

$ ./gradlew -version

------------------------------------------------------------
Gradle 4.7
------------------------------------------------------------

Build time:   2018-04-18 09:09:12 UTC
Revision:     b9a962bf70638332300e7f810689cb2febbd4a6c

Groovy:       2.4.12
Ant:          Apache Ant(TM) version 1.9.9 compiled on February 2 2017
JVM:          1.8.0_162 (Oracle Corporation 25.162-b12)
OS:           Mac OS X 10.13.4 x86_64

Any clues or tips are more than welcome :)

Thanks!

Answer 1

Upgrading the google-services plugin to version 4.0.1 fixed the issue.

From the Firebase sdk changelog page: https://firebase.google.com/support/release-notes/android

In other words, change this:

classpath 'com.google.gms:google-services:4.0.0'

to this:

classpath 'com.google.gms:google-services:4.0.1'