Estoy tratando de generar APK firmado usando AndroidStudio pero me sale este error:

    Error:A problem was found with the configuration of task ':app:packageRelease'.
> File 'com.pachu.fartsound' specified for property 'signingConfig.storeFile' does not exist.

No sé si lo necesitas pero ahí está mi build.gradle:

    apply plugin: 'com.android.application'
apply plugin: 'android'
android {
    compileSdkVersion 19
    buildToolsVersion "20.0.0"

    defaultConfig {
        applicationId "com.pachu.fartsounds"
        minSdkVersion 9
        targetSdkVersion 19
        versionCode 1
        versionName "1.2"
    }
    buildTypes {
        release {
            runProguard false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile 'com.android.support:appcompat-v7:19.+'
    compile 'com.google.android.gms:play-services:5.0.89'
}