Get token return null

I’m building push notification by (ionic3 and firebase) , when running on emulator (genymotion api19) gettoken() return null , when running on device or other emulator getToken() return the token successfully.
Is that an error in my app or in the emulator ?

The cordova-plugin-firebase is broken in cordova 7.0.0

Use any of the below methods for resolving the issue.

Installation command for cordova android version 7 and above:
"cordova plugin add cordova-plugin-firebase --variable ANDROID_VERSION=7x --save"

Installation command for cordova android version 6 and below:
"cordova plugin add cordova-plugin-firebase --variable ANDROID_VERSION=6x --save"


plugins/cordova-plugin-firebase/scripts/after_prepare.js line 51
node_modules/cordova-plugin-firebase/scripts/after_prepare.js line 51

-        stringsXml: ANDROID_DIR + '/res/values/strings.xml'
+        stringsXml: fileExists(ANDROID_DIR + '/app/src/main/res/values/strings.xml') ? ANDROID_DIR + '/app/src/main/res/values/strings.xml' : ANDROID_DIR + '/res/values/strings.xml'