problem androis studio 3.2 with Backendless

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Main activity
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package com.imanuel.mybackendless;

import android.content.Context;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.Toast;

import com.backendless.Backendless;
import com.backendless.BackendlessUser;
import com.backendless.async.callback.AsyncCallback;
import com.backendless.exceptions.BackendlessFault;

public class MainActivity extends AppCompatActivity {
    Context context;
    EditText txtUser,txtPass;
    ProgressBar progressBar;

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

    private void setPointer() {
        this.context=this;
        //create connection to the Backendless with app id and app key!!!
        Backendless.initApp(context,getString(R.string.app_id),getString(R.string.app_key));

        txtUser=findViewById(R.id.lblUserName);
        txtPass=findViewById(R.id.lblUserPass);
        progressBar= findViewById(R.id.pb);

        findViewById(R.id.btnLoging).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                progressBar.setVisibility(View.VISIBLE);
                makeLogin();
            }
        });

        findViewById(R.id.btnRegister).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                progressBar.setVisibility(View.VISIBLE);
                makeRegister();
            }
        });
    }

    private void makeRegister() {
        //first send instance of user
        BackendlessUser user = new BackendlessUser();
        user.setProperty("email", txtUser.getText().toString());
        String userName[] = txtUser.getText().toString().split("@");
        user.setProperty("name",userName[0]);
        user.setPassword(txtPass.getText().toString());

        Backendless.UserService.register(user, new AsyncCallback<BackendlessUser>() {
            @Override
            public void handleResponse(BackendlessUser response) {
                Toast.makeText(context,"all is OK", Toast.LENGTH_SHORT).show();
                progressBar.setVisibility(View.INVISIBLE);
            }

            @Override
            public void handleFault(BackendlessFault fault) {
                progressBar.setVisibility(View.INVISIBLE);
                Toast.makeText(context,fault.getMessage(),Toast.LENGTH_LONG).show();
                Log.e("register","handlerFault"+fault.getMessage());
            }
        });
        txtUser.setText("");
        txtUser.setText("");
    }

    private void makeLogin() {
        Backendless.UserService.login(txtUser.getText().toString(), txtPass.getText().toString(), new AsyncCallback<BackendlessUser>() {
            @Override
            public void handleResponse(BackendlessUser response) {
                Toast.makeText(context,"user logged", Toast.LENGTH_SHORT).show();
                progressBar.setVisibility(View.INVISIBLE);
            }

            @Override
            public void handleFault(BackendlessFault fault) {
                progressBar.setVisibility(View.INVISIBLE);
                Toast.makeText(context,fault.getMessage(), Toast.LENGTH_LONG).show();
                Log.e("error login", "handler Fault"+fault.getMessage());
            }
        });

    }
}


---------------
gradle
---------------


apply plugin: 'com.android.application'

android {
    compileSdkVersion 27
    defaultConfig {
        applicationId "com.imanuel.mybackendless"
        minSdkVersion 21
        targetSdkVersion 27
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'com.android.support:appcompat-v7:27.1.1'
    implementation group: 'com.backendless', name: 'backendless', version: '5.0.2'
    implementation ( group: 'io.socket', name: 'socket.io-client', version: '1.0.0' ) {
        //      excluding org.json which is provided by Android
        exclude group: 'org.json', module: 'json'
    }
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
}