Null Object Reference when with Android App

Question

I am following this video tutorial on building an Android App that uploads a PDF to Google Drive, I have finished the tutorial but the following error is being thrown when I press the button:

2021-01-03 20:36:48.895 8669-8669/com.indigo.green E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.indigo.green, PID: 8669
    java.lang.IllegalStateException: Could not execute method for android:onClick
        at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:414)
        at android.view.View.performClick(View.java:7862)
        at android.widget.TextView.performClick(TextView.java:15004)
        at android.view.View.performClickInternal(View.java:7831)
        at android.view.View.access$3600(View.java:879)
        at android.view.View$PerformClick.run(View.java:29359)
        at android.os.Handler.handleCallback(Handler.java:883)
        at android.os.Handler.dispatchMessage(Handler.java:100)
        at android.os.Looper.loop(Looper.java:237)
        at android.app.ActivityThread.main(ActivityThread.java:8167)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:496)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1100)
     Caused by: java.lang.reflect.InvocationTargetException
        at java.lang.reflect.Method.invoke(Native Method)
        at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:409)
        at android.view.View.performClick(View.java:7862) 
        at android.widget.TextView.performClick(TextView.java:15004) 
        at android.view.View.performClickInternal(View.java:7831) 
        at android.view.View.access$3600(View.java:879) 
        at android.view.View$PerformClick.run(View.java:29359) 
        at android.os.Handler.handleCallback(Handler.java:883) 
        at android.os.Handler.dispatchMessage(Handler.java:100) 
        at android.os.Looper.loop(Looper.java:237) 
        at android.app.ActivityThread.main(ActivityThread.java:8167) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:496) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1100) 
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.android.gms.tasks.Task com.indigo.green.DriveServiceHelper.createFilePDF(java.lang.String)' on a null object reference
        at com.indigo.green.MainActivity.uploadPdfFile(MainActivity.java:106)
        at java.lang.reflect.Method.invoke(Native Method) 
        at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:409) 
        at android.view.View.performClick(View.java:7862) 
        at android.widget.TextView.performClick(TextView.java:15004) 
        at android.view.View.performClickInternal(View.java:7831) 
        at android.view.View.access$3600(View.java:879) 
        at android.view.View$PerformClick.run(View.java:29359) 
        at android.os.Handler.handleCallback(Handler.java:883) 
        at android.os.Handler.dispatchMessage(Handler.java:100) 
        at android.os.Looper.loop(Looper.java:237) 
        at android.app.ActivityThread.main(ActivityThread.java:8167) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:496) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1100) 

I am not really sure what's going on so any guidance would be great.

My MainActivity:

package com.indigo.green;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;

import android.app.ProgressDialog;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;

import com.google.android.gms.auth.api.signin.GoogleSignIn;
import com.google.android.gms.auth.api.signin.GoogleSignInAccount;
import com.google.android.gms.auth.api.signin.GoogleSignInClient;
import com.google.android.gms.auth.api.signin.GoogleSignInOptions;
import com.google.android.gms.common.api.Scope;
import com.google.android.gms.tasks.OnFailureListener;
import com.google.android.gms.tasks.OnSuccessListener;
import com.google.api.client.extensions.android.http.AndroidHttp;
import com.google.api.client.googleapis.extensions.android.gms.auth.GoogleAccountCredential;
import com.google.api.client.json.gson.GsonFactory;
import com.google.api.services.drive.Drive;
import com.google.api.services.drive.DriveScopes;

import java.util.Collections;


public class MainActivity extends AppCompatActivity {
    DriveServiceHelper driveServiceHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        requestSignIn();

    }

    private void requestSignIn()
    {
        GoogleSignInOptions signInOptions = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
                .requestEmail()
                .requestScopes(new Scope(DriveScopes.DRIVE_FILE))
                .build();

        GoogleSignInClient client = GoogleSignIn.getClient(this,signInOptions);

        startActivityForResult(client.getSignInIntent(), 400);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        switch (requestCode)
        {
            case 400:
                if(requestCode == RESULT_OK)
                {
                    handleSignIntent(data);
                }
                break;
        }
    }

    private void handleSignIntent(Intent data) {
        GoogleSignIn.getSignedInAccountFromIntent(data)
                .addOnSuccessListener(new OnSuccessListener<GoogleSignInAccount>() {
                    @Override
                    public void onSuccess(GoogleSignInAccount googleSignInAccount) {

                        GoogleAccountCredential credential = GoogleAccountCredential.usingOAuth2(MainActivity.this, Collections.singleton(DriveScopes.DRIVE_FILE));

                        credential.setSelectedAccount(googleSignInAccount.getAccount());

                        Drive googleDriveService = new Drive.Builder(
                            AndroidHttp.newCompatibleTransport(),
                            new GsonFactory(),
                            credential)
                                .setApplicationName("My Drive Tutorial")
                                .build();

                        driveServiceHelper = new DriveServiceHelper(googleDriveService);

                    }
                })
                .addOnFailureListener(new OnFailureListener() {
                    @Override
                    public void onFailure(@NonNull Exception e) {

                    }
                });
    }


    public void uploadPdfFile(View v)
    {
        ProgressDialog progressDialog = new ProgressDialog(MainActivity.this);
        progressDialog.setTitle("Uploading to Google Drive");
        progressDialog.setMessage("Please wait...");
        progressDialog.show();

        String filePath = "/storage/emulated/0/Nike-Run-Club-Marathon-Training-Plan.pdf";

        driveServiceHelper.createFilePDF(filePath).addOnSuccessListener(new OnSuccessListener<String>() {
            @Override
            public void onSuccess(String s) {
                progressDialog.dismiss();
                Toast.makeText(getApplicationContext(), "Uploaded successfully", Toast.LENGTH_LONG).show();
            }
        })
                .addOnFailureListener(new OnFailureListener() {
                    @Override
                    public void onFailure(@NonNull Exception e) {
                        progressDialog.dismiss();
                        Toast.makeText(getApplicationContext(), "Check your google drive api key", Toast.LENGTH_LONG).show();
                    }
                });
    }

}

The DriveServiceHelper class:

package com.indigo.green;

import com.google.android.gms.tasks.Task;
import com.google.android.gms.tasks.Tasks;
import com.google.api.client.http.FileContent;
import com.google.api.services.drive.Drive;
import com.google.api.services.drive.model.File;


import java.io.IOException;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;

public class DriveServiceHelper
{
    private final Executor mExecutor = Executors.newSingleThreadExecutor();
    private Drive mDriveService;

    public DriveServiceHelper(Drive mDriveService){
        this.mDriveService = mDriveService;

    }

    public Task<String> createFilePDF(String filePath)
    {
        return Tasks.call(mExecutor, () ->{

            File fileMetaData = new File();
            fileMetaData.setName("MyPDFFile");

            java.io.File file = new java.io.File(filePath);

            FileContent mediaContent = new FileContent("application/pdf", file);

            File myFile = null;

            try
            {
                myFile = mDriveService.files().create(fileMetaData, mediaContent).execute();
            } catch (Exception e) {

                e.printStackTrace();
            }

            if(myFile == null) {

                throw new IOException("Null result when requesting file creation");
            }

            return myFile.getId();

        });
    }
}

My build Gradle app file:

apply plugin: 'com.android.application'

android {
    compileSdkVersion 30
    buildToolsVersion "30.0.0"
    defaultConfig {
        applicationId "com.indigo.green"
        minSdkVersion 24
        targetSdkVersion 30
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled true
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }

    compileOptions
            {
                sourceCompatibility JavaVersion.VERSION_1_8
                targetCompatibility JavaVersion.VERSION_1_8
    }

    packagingOptions {
        exclude 'META-INF/DEPENDENCIES'
    }


}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'androidx.appcompat:appcompat:1.2.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test:runner:1.3.0'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'

    implementation 'com.google.android.gms:play-services-auth:19.0.0'

    implementation ('com.google.apis:google-api-services-drive:v3-rev136-1.25.0')
            {
                exclude group: 'org.apache.httpcomponents'
            }

    implementation ('com.google.api-client:google-api-client-android:1.26.0')
            {
                exclude group: 'org.apache.httpcomponents'
            }

    implementation ('com.google.http-client:google-http-client-gson:1.26.0')
}

Build gradle project file:

buildscript {
    repositories {
        google()
        jcenter()
        maven {
            url 'https://maven.google.com/'
            name 'Google'
        }

        
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.4.2'
        
        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        google()
        jcenter()
        
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

activity.main:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/button"
        android:layout_width="221dp"
        android:layout_height="82dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginBottom="8dp"
        android:text="Upload File"
        android:textStyle="bold"
        android:onClick="uploadPdfFile"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.812" />
</androidx.constraintlayout.widget.ConstraintLayout>

manifest:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.indigo.green">

    <uses-permission android:name="android.permission.INTERNET"></uses-permission>
    <uses-permission android:name="android.permission.GET_ACCOUNTS"></uses-permission>
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"></uses-permission>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>