Null object reference when I try to build room

Question

I want to build room in Kotlin using my function getDatabase(context) and I have this error :

W/System.err: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Package.getName()' on a null object reference
W/System.err:     at android.arch.persistence.room.Room.getGeneratedImplementation(Room.java:77)

This is very strange because it's the first time I have this error (I use Room in other project and I don't have this bug). The app don't crash but the database is not working.

I try looking in internet but I don't see nothing about this bug (only this japanese guy : https://teratail.com/questions/118177 but I don't understand japanese).

AppDatabase :

@Database(entities = [(Wallet::class), (Historique::class)], version = 1)
abstract class AppDatabase : RoomDatabase() {
    abstract fun walletDao(): WalletDao
    abstract fun historiqueDao(): HistoriqueDao
}

private var INSTANCE: AppDatabase? = null

fun getDatabase(context: Context?): AppDatabase {
    if (INSTANCE == null)
        INSTANCE = context?.let { Room.databaseBuilder(context, AppDatabase::class.java, DATABASE_NAME).build() }
    return INSTANCE as AppDatabase
}

This is my Gradle :

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

android {
    compileSdkVersion 27
    defaultConfig {
        applicationId "my.app"
        minSdkVersion 19
        targetSdkVersion 27
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
    implementation 'com.android.support:appcompat-v7:27.1.1'
    implementation 'com.android.support.constraint:constraint-layout:1.1.0'
    implementation 'com.android.support:support-v4:27.1.1'

    implementation "android.arch.persistence.room:runtime:1.0.0"
    annotationProcessor "android.arch.persistence.room:compiler:1.0.0"
    kapt "android.arch.persistence.room:compiler:1.0.0"

    implementation "org.jetbrains.anko:anko-commons:0.10.4"
    implementation "org.jetbrains.anko:anko-design:0.10.4"
    implementation "com.chibatching.kotpref:kotpref:2.5.0"
    implementation "com.chibatching.kotpref:initializer:2.5.0"
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.1'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.1'
}

I think you are using wrong Package, you want to use ContextWrapper's packageName instead of java.Lang.Package. Can you check that ? — Ezio, Apr 13 '18 at 10:40
Can you add the code in which you invoke `getDatabase` method? — Michał Pawlik, Apr 13 '18 at 21:54

score 7 · Answer 1 · answered Oct 12 '19 at 12:44

7

I have encountered the same problem. The simple solution would be is to go to your database class and check if the package is set in the top of the file

Example:

package com.example.app

This will set which package this class belongs to.

answered Oct 12 '19 at 12:44

Jeprox

71
1
4

score 1 · Answer 2 · answered Oct 02 '19 at 20:21

I had the same problem, thanks to @Jéwôm', the link he provided - https://teratail.com/questions/118177 and Google Translator I found a solution.

That japanese guy whom Jéwôm' mentioned found out that this bug occured because of damaged/wrong directory structure in project files.

His directory seemed like this:

app  
   |-manifests  
   |-java  
     |-com.example.user.applyName
       |-MainActivity
       |-SubActivity // インスタンスを生成するActivity
     |-AppDatabase
     |-Dairy
     |-DairyDao
    |-res

And he solved the problem by moving files "AppDatabase", "Dairy" and "DairyDao" to the same folder as "MainActivity" and "SubActivity".

In my case I didn't have badly structured directory structure, but I moved all kotlin files to other folder (in my case from "com.example.myAppName" to "com.example.myAppName (androidTest)" and then moved them back (back to "com.example.myAppName"). Then I rebuilt that project. This somehow worked for me.

score 0 · Accepted Answer · answered Apr 30 '18 at 07:51

0

The problem was from some imports (by coping the class from an other project).

answered Apr 30 '18 at 07:51

Jéwôm'

3,753
5
40
73

I have got the same problem but have no any clue. Could you give some guidelines where to look at? – sunflower20 Jul 13 '18 at 13:37

Null object reference when I try to build room

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