Do not attempt to use google json (firebase) in a gradle library. The google-service plugin is made for applications only.

Otherwise you'll get obscure compilation errors.

gradle/wrapper/gradle-wrapper.properties

@@ -3,4 +3,5 @@ distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.4-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.7-all.zip
+

linphoneAndroidSdk.gradle

@@ -1,12 +1,8 @@
 // Project information
 buildDir = 'bin'
-def firebaseEnable() {
-    File googleFile = new File('google-services.json')
-    return googleFile.exists()
-}
+
 
 buildscript {
-    File googleFile = new File('google-services.json')
     repositories {
         jcenter()
         mavenCentral()
@@ -15,9 +11,6 @@ buildscript {
     }
     dependencies {
         classpath 'com.android.tools.build:gradle:3.1.0'
-        if (googleFile.exists()) {
-            classpath 'com.google.gms:google-services:3.1.0'
-        }
     }
 }
 
@@ -34,16 +27,7 @@ apply plugin: 'com.android.library'
 
 dependencies {
     compile group: 'org.apache.commons', name: 'commons-compress', version: '+'
-    if (firebaseEnable()) {
-        compile 'com.google.firebase:firebase-messaging:11.+'
-    } else {
-        compile fileTree(include: 'gcm.jar', dir: 'libs')
-        compile 'com.android.support:support-v4:+'
-    }
-}
-
-if (firebaseEnable()) {
-    apply plugin: 'com.google.gms.google-services'
+    compile 'com.android.support:support-v4:26.0.2'
 }
 
 
@@ -56,11 +40,9 @@ def srcDirs = ['submodules/mediastreamer2/java/src',
 
 def excludeFiles = []
 // Exclude firebase file if not enable
-if (!firebaseEnable()) {
-    excludeFiles.add('**/Firebase*')
-} else {
-    excludeFiles.add('**/gcm*')
-}
+
+excludeFiles.add('**/Firebase*')
+excludeFiles.add('**/gcm*')
 excludeFiles.add('**/mediastream/MediastreamerActivity.java')
 
 def excludePackage = []