Why is the error "Unfortunate, has stopped" displayed?

Question

Android

Good day. I recently started working on firebase and launched the project. But I got an error Unfortunately MyApplication,has stopped. Here is the code:

package com.example.admin.myapplicatio;

import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;


import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    Button btnAdd, btnRead, btnClear;
    EditText etName, etEmail;

    DBHelper dbHelper;
    private FirebaseAuth mAuth;
    private FirebaseAuth.AuthStateListener mAuthListener;
    private EditText ETemail;
    private EditText ETpassword;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mAuth = FirebaseAuth.getInstance();

        mAuthListener = new FirebaseAuth.AuthStateListener() {
            @Override
            public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
                FirebaseUser user = firebaseAuth.getCurrentUser();
                if(user != null){

                }else{

                }
            }
        };
        ETemail = (EditText) findViewById(R.id.et_email);
        ETpassword = (EditText) findViewById(R.id.et_password);

        findViewById(R.id.btn_sign_in).setOnClickListener(this);
        findViewById(R.id.btn_registration).setOnClickListener(this);
    }

    @Override
    public void onClick(View view) {
        if(view.getId() == R.id.btn_sign_in)
        {
            signin(ETemail.getText().toString(),ETpassword.getText().toString());
        }else if (view.getId() == R.id.btn_registration)
        {
            registration(ETemail.getText().toString(),ETpassword.getText().toString());
        }

    }

    public void signin(String email , String password)
    {
        mAuth.signInWithEmailAndPassword(email,password).addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
            @Override
            public void onComplete(@NonNull Task<AuthResult> task) {
                if(task.isSuccessful()) {
                    Toast.makeText(MainActivity.this, "Aвторизация успешна", Toast.LENGTH_SHORT).show();
                }else
                    Toast.makeText(MainActivity.this, "Aвторизация провалена", Toast.LENGTH_SHORT).show();

            }
        });
    }
    public void registration (String email , String password){
        mAuth.createUserWithEmailAndPassword(email, password).addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
            @Override
            public void onComplete(@NonNull Task<AuthResult> task) {
                if(task.isSuccessful())
                {
                    Toast.makeText(MainActivity.this, "Регистрация успешна", Toast.LENGTH_SHORT).show();
                }
                else
                    Toast.makeText(MainActivity.this, "Регистрация провалена", Toast.LENGTH_SHORT).show();
            }
        });
    }
}

And the DBHelper code:

package com.example.admin.myapplicatio;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DBHelper  extends SQLiteOpenHelper{

    public static final int DATABASE_VERSION = 1;
    public static final String DATABASE_NAME = "contactDb";
    public static final String TABLE_CONTACTS = "contacts";

    public static final String KEY_ID = "_id";
    public static final String KEY_NAME = "name";
    public static final String KEY_MAIL = "mail";

    public DBHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("create table " + TABLE_CONTACTS + "(" + KEY_ID
                + " integer primary key," + KEY_NAME + " text," + KEY_MAIL + " text" + ")");

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("drop table if exists " + TABLE_CONTACTS);

        onCreate(db);

    }
}

Here is the xml file:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_authentication"
    android:layout_width="match_parent"
    android:layout_height="match_parent">




    <EditText android:layout_width="250dp"
        android:layout_height="50dp"
        android:id="@+id/et_email"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="145dp"
        android:hint="Email"
        android:textColorHint="@color/colorPrimary"
        android:textSize="30dp"/>
    <EditText android:layout_width="250dp"
        android:layout_height="50dp"
        android:layout_centerHorizontal="true"
        android:layout_below="@+id/et_email"
        android:hint="Password"
        android:textColorHint="@color/colorPrimary"
        android:textSize="30dp"
        android:id="@+id/et_password"
        />

    <LinearLayout android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/et_password"
        android:layout_marginTop="20dp"
        >
        <Button android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:text="Авторизация"
            android:layout_weight="1"
            android:id="@+id/btn_sign_in"/>
        <Button android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="Регистрация"
            android:id="@+id/btn_registration"/>

    </LinearLayout>
</RelativeLayout>

And here is the error itself:
What is the matter and how can I fix the error?