Error while compiling code for firebase admin

I got an error while compiling code for Firebase admin.

Error:

Following the info from <http://www.slf4j.org/codes.html#StaticLoggerBinder> I've tried adding all the dependencies one by one

adding

testCompile group: 'org.apache.logging.log4j', name: 'log4j-slf4j-impl', version: '2.13.3'

or

testCompile group: 'org.slf4j', name: 'slf4j-nop', version: '1.8.0-beta4'

or

testCompile group: 'org.slf4j', name: 'slf4j-simple', version: '1.8.0-beta4'

or

testCompile group: 'org.slf4j', name: 'slf4j-jdk14', version: '1.8.0-beta4'

or

testCompile group: 'ch.qos.logback', name: 'logback-classic', version: '1.2.3'

doesn't remove the error.
May I know what I'm going wrong with?

My Gradle file:

plugins {
    id 'java'
}

group 'org.example'
version '1.0-SNAPSHOT'

sourceCompatibility = 1.8

repositories {
    mavenCentral()
}

dependencies {
    testCompile group: 'junit', name: 'junit', version: '4.12'
    implementation 'com.google.firebase:firebase-admin:6.13.0'
//None of these seem to remove the error
//    testCompile group: 'org.apache.logging.log4j', name: 'log4j-slf4j-impl', version: '2.13.3'
//    testCompile group: 'org.slf4j', name: 'slf4j-nop', version: '1.8.0-beta4'
//    testCompile group: 'org.slf4j', name: 'slf4j-simple', version: '1.8.0-beta4'
//    testCompile group: 'org.slf4j', name: 'slf4j-jdk14', version: '1.8.0-beta4'
//    testCompile group: 'ch.qos.logback', name: 'logback-classic', version: '1.2.3'

My main Class

import com.google.auth.oauth2.GoogleCredentials;
import com.google.firebase.FirebaseApp;
import com.google.firebase.FirebaseOptions;
import com.google.firebase.database.*;

import java.io.IOException;

public class MainClass {
    public static void main(String[] args) throws IOException {
        FirebaseOptions options = new FirebaseOptions.Builder()
                .setCredentials(GoogleCredentials.getApplicationDefault())
                .setDatabaseUrl("https://{my database name}.firebaseio.com/")
                .build();

        FirebaseApp.initializeApp(options);
        DatabaseReference ref = FirebaseDatabase.getInstance()
                .getReference("restricted_access/secret_document");
        ref.setValue("hiIII", new DatabaseReference.CompletionListener() {
            @Override
            public void onComplete(DatabaseError error, DatabaseReference ref) {
                System.out.println("Completed");
            }
        });
    }
}

May I know What I'm going wrong with? and How can I Correct it?

This warning message is reported when the org.slf4j.impl.StaticLoggerBinder class could not be loaded into memory. This happens when no appropriate SLF4J binding could be found on the class path. Placing one (and only one) of slf4j-nop.jar slf4j-simple.jar, slf4j-log4j12.jar, slf4j-jdk14.jar or logback-classic.jar on the class path should solve the problem.

If this problem doesnot solve try clear caches and restart.