Unresolved reference on 1.2.0 in Android Studio

Android
1

Unresolved reference: endsWith Error in below code

var baseUrl = "http://api.foobar.com/v1"
if (!baseUrl.endsWith("/"))
 baseUrl = baseUrl + "/"

What is the cause?
There was no problem when it was use 1.1.60.

Below is build.gradle

buildscript {
 ext.kotlin_version = '1.2.0'
 repositories {
 jcenter()
 google()
 }
 dependencies {
 classpath 'com.android.tools.build:gradle:3.0.1'
 classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"

 // NOTE: Do not place your application dependencies here; they belong
 // in the individual module build.gradle files
 }
}

apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-kapt'

android {
    //...
}

dependencies {
    compile "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
}
2

No problems with mine. I’m using Kolin 1.2.0 with Android Studio 3.0.1.