You import wrong BuildConfig file

Remove your BuildConfig import & re-import your app module BuildConfig

In my app I need to fetch the app version code and name so I was using below statement.

 obj.setCurrentVersion("APP " + 
 String.valueOf(BuildConfig.VERSION_NAME));

It was working fine and returns correct result.
But now it’s return empty string once i checked BuildConfig class all the values are empty.

public final class BuildConfig {
    public static final boolean DEBUG = false;
    public static final java.lang.String APPLICATION_ID = "androidx.multidex";
    public static final java.lang.String BUILD_TYPE = "release";
    public static final java.lang.String FLAVOR = "";
    public static final int VERSION_CODE = -1;
    public static final java.lang.String VERSION_NAME = "";

    public BuildConfig() { /* compiled code */ }
}
     

Build_gradle file

apply plugin: 'com.android.application'

android {
    signingConfigs {
        config {
         
        }
    }
    compileSdkVersion 28
    defaultConfig {
        applicationId "com.app.application"
        minSdkVersion 21 //21
        targetSdkVersion 28
        versionCode 16 //15
        versionName "2.0.4"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        multiDexEnabled true
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }

    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }

Why is that happening and how to fix it?