title: Room Kotlin:Entities and Pojos must have a usable public constructor
body: <p>When I run my app,I got follow error.</p>
  
  <pre><code>Error: Entities and Pojos must have a usable public constructor. You can have an empty
    constructor or a constructor whose parameters match the fields (by name and type).
    Tried the following constructors but they failed to match:
    ChatMsg(java.lang.String,int) : [arg0 : null, arg1 : null]
  Error: Entities and Pojos must have a usable public constructor. You can have an empty
    constructor or a constructor whose parameters match the fields (by name and type).
  Error: Entities and Pojos must have a usable public constructor. You can have an empty
    constructor or a constructor whose parameters match the fields (by name and type).
    Tried the following constructors but they failed to match:
    ChatMsg(java.lang.String,int) : [arg0 : null, arg1 : null]
  Error: Entities and Pojos must have a usable public constructor. You can have an empty
    constructor or a constructor whose parameters match the fields (by name and type).
  Warning: Schema export directory is not provided to the annotation processor so we cannot export the schema. You can either provide `room.schemaLocation` annotation processor argument OR set exportSchema to false.
  </code></pre>
  
  <p>That's my build.gradle for project</p>
  
  <pre><code>buildscript {
      ext.kotlin_version = '1.1.2-4'
      repositories {
          maven { url 'https://maven.google.com' }
          jcenter()  
      }
      dependencies {
          classpath 'com.android.tools.build:gradle:3.0.0-alpha4'
          classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
          classpath 'com.letv.sarrsdesktop:BlockCanaryExPlugin:0.9.9.2'
  
      }
  }   
  allprojects {
      repositories {
          jcenter()
          maven { url 'https://maven.google.com' }
          maven { url "https://jitpack.io" }
          mavenCentral()
      }
  }
  
  task clean(type: Delete) {
      delete rootProject.buildDir
  }
  </code></pre>
  
  <p>That's my build.gradle for module</p>
  
  <pre><code>apply plugin: 'com.android.application'
  apply plugin: 'kotlin-android'
  kapt {
      generateStubs = true
  }
  android {
      compileSdkVersion 25
      buildToolsVersion "25.0.2"
      defaultConfig {
          applicationId "cn.sz.cyrus.kotlintest"
          minSdkVersion 14
          targetSdkVersion 25
          versionCode 1
          versionName "1.0"
          testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
  
          javaCompileOptions{
              annotationProcessorOptions{
                  includeCompileClasspath = true
              }
          }
      }
  
      buildTypes {
          release {
              minifyEnabled false
              proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
          }
      }
  }
  
  
  dependencies {
      compile fileTree(include: ['*.jar'], dir: 'libs')
      androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
          exclude group: 'com.android.support', module: 'support-annotations'
      })
      compile "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
      compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
      compile 'com.android.support:appcompat-v7:25.3.1'
      testCompile 'junit:junit:4.12'
      compile 'com.android.support:design:25.3.1'
      compile 'com.android.support.constraint:constraint-layout:1.0.2'
      debugCompile 'com.squareup.leakcanary:leakcanary-android:1.5.1'
      releaseCompile 'com.squareup.leakcanary:leakcanary-android-no-op:1.5.1'
      testCompile 'com.squareup.leakcanary:leakcanary-android-no-op:1.5.1'
      compile 'com.github.GrenderG:Toasty:1.2.5'
      compile 'com.orhanobut:logger:1.15'
      compile 'io.reactivex.rxjava2:rxandroid:2.0.1'
      compile 'com.umeng.analytics:analytics:latest.integration'
      compile 'com.github.kittinunf.fuel:fuel-android:1.7.0' //for Android
      compile 'com.github.kittinunf.fuel:fuel-rxjava:1.7.0' //for RxJava support
      compile "android.arch.persistence.room:runtime:1.0.0-alpha3"
      annotationProcessor "android.arch.persistence.room:compiler:1.0.0-alpha3"
      kapt "android.arch.persistence.room:compiler:1.0.0-alpha3"
      compile "android.arch.persistence.room:rxjava2:1.0.0-alpha3" 
  }
  </code></pre>
  
  <p>That's my pojo class</p>
  
  <pre><code>@Entity
  data class ChatMsg(var msg: String,
                var to: Int) {
  
      companion object TO {
          val MASTER = 0
          val ROBOT = 1
      }
  
      @PrimaryKey(autoGenerate = true)
      var id: Int = 0
      var createTime: Long = System.currentTimeMillis()
      var translMsg: String = ""
  }
  </code></pre>
  
  <p>I have google my problem,but results seems can't answer my question.Who has ideas for this question . Thanks for first!</p>