"Cannot add a configuration with name 'endpoints' as a configuration..." - google-app-engine

Question

I am trying to migrate to GAE framework 2.0. As I follow the document, I realised that when I add this line to build.gradle.
apply plugin: 'com.google.cloud.tools.endpoints-framework-server'
I can this error message:
Error:Cannot add a configuration with name 'endpoints' as a
configuration with that name already exists.
Did anyone encounter the same error?
My build.gradle is below:
buildscript {
repositories {
mavenCentral()
jcenter()
}
dependencies {
classpath 'com.google.appengine:gradle-appengine-plugin:+'
classpath 'com.google.cloud.tools:endpoints-framework-gradle-plugin:+'
}
}
repositories {
mavenCentral()
jcenter()
}
apply plugin: 'java'
apply plugin: 'war'
apply plugin: 'appengine'
apply plugin: 'com.google.cloud.tools.endpoints-framework-server'
sourceCompatibility = JavaVersion.VERSION_1_7
targetCompatibility = JavaVersion.VERSION_1_7
dependencies {
appengineSdk 'com.google.appengine:appengine-java-sdk:1.9.56'
testCompile 'junit:junit:4.12'
testCompile 'com.google.appengine:appengine-testing:1.9.56'
testCompile 'com.google.appengine:appengine-api-stubs:1.9.56'
// 2.0
compile group: 'com.google.endpoints', name: 'endpoints-framework', version: '+'
compile group: 'com.googlecode.junit-toolbox', name: 'junit-toolbox', version: '1.5'
compile 'com.google.appengine:appengine-endpoints:1.9.50'
compile 'com.google.appengine:appengine-endpoints-deps:1.9.50'
compile 'com.googlecode.objectify:objectify:5.1.5'
compile 'org.json:json:20151123'
compile 'javax.servlet:servlet-api:2.5'
compile 'org.apache.httpcomponents:httpclient:4.5.2'
compile 'com.ganyo:gcm-server:1.0.2'
compile 'com.google.appengine.tools:appengine-gcs-client:0.4.4'
//compile 'commons-fileupload:commons-fileupload:1.3.1'
compile 'com.google.apis:google-api-services-storage:v1-rev66-1.21.0'
}
appengine {
downloadSdk = true
appcfg {
oauth2 = true
}
endpoints {
getClientLibsOnBuild = true
getDiscoveryDocsOnBuild = true
}
httpAddress = "0.0.0.0"
}

Answer 1

The appengine plugin you've already applied already creates a configuration named endpoints - see here. Are you sure that both plugins, I mean appengine and com.google.cloud.tools.endpoints-framework-server can be used together in a project? Since there might be only one configuration with particular name.