title: Android - NullPointerException Attempt to invoke virtual method 'com.google.android.gms.tasks.Task
body: <p>Trying to set up a simple app that uses Firebase Auth to handle Registration/Login of a user. This issue is quite confusing as the outcome is different on my physical testing device (HTC M8 7.1.1) and Emulator (5P 7.1.1).</p>
  
  <p>On the emulator, I get the following error when I click my Login or Register Buttons. </p>
  
  <pre><code>                                                                --------- beginning of crash
  03-02 03:24:20.625 3002-3002/com.mad.losesano E/AndroidRuntime: FATAL EXCEPTION: main
                                                                  Process: com.mad.losesano, PID: 3002
                                                                  java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.android.gms.tasks.Task com.google.android.gms.common.api.GoogleApi.zzb(com.google.android.gms.common.api.internal.zzdd)' on a null object reference
                                                                      at com.google.android.gms.internal.zzdvv.zzb(Unknown Source)
                                                                      at com.google.android.gms.internal.zzdwc.zzb(Unknown Source)
                                                                      at com.google.firebase.auth.FirebaseAuth.signInWithEmailAndPassword(Unknown Source)
                                                                      at com.mad.losesano.LoginActivity.userLogin(LoginActivity.java:69)
                                                                      at com.mad.losesano.LoginActivity.onClick(LoginActivity.java:105)
                                                                      at android.view.View.performClick(View.java:5637)
                                                                      at android.view.View$PerformClick.run(View.java:22429)
                                                                      at android.os.Handler.handleCallback(Handler.java:751)
                                                                      at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                      at android.os.Looper.loop(Looper.java:154)
                                                                      at android.app.ActivityThread.main(ActivityThread.java:6119)
                                                                      at java.lang.reflect.Method.invoke(Native Method)
                                                                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
  </code></pre>
  
  <p>On my physical device, when I register a user, it works as expected. The user account can be seen in the firebase console. When I click 'login' on the this device, nothing happens. It seems that it doesn't even enter the OnClick method (tested by running a Log.d message in the OnClick method which doesn't show up when I click the button).</p>
  
  <p>Here is the LoginActivity Code</p>
  
  <pre><code>package com.mad.losesano;
  
          import android.app.Activity;
          import android.content.Intent;
          import android.support.annotation.NonNull;
          import android.os.Bundle;
          import android.util.Log;
          import android.util.Patterns;
          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;
  
  public class LoginActivity extends Activity implements View.OnClickListener {
  
      FirebaseAuth mAuth;
      EditText et_email, et_password;
      Button login_button;
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_login);
  
          mAuth = FirebaseAuth.getInstance();
  
          et_email = (EditText) findViewById(R.id.email_et_login);
          et_password = (EditText) findViewById(R.id.password_et_login);
  
          findViewById(R.id.register_tv).setOnClickListener(this);
          login_button = (Button) findViewById(R.id.login_button);
          login_button.setOnClickListener(this);
  
      }
  
      private void userLogin() {
          String email = et_email.getText().toString().trim();
          String password = et_password.getText().toString().trim();
  
          if (email.isEmpty()) {
              et_email.setError("Email is required");
              et_email.requestFocus();
              return;
          }
  
          if (!Patterns.EMAIL_ADDRESS.matcher(email).matches()) {
              et_email.setError("Please enter a valid email");
              et_email.requestFocus();
              return;
          }
  
          if (password.isEmpty()) {
              et_password.setError("Password is required");
              et_password.requestFocus();
              return;
          }
  
          if (password.length() &lt; 6) {
              et_password.setError("Minimum lenght of password should be 6");
              et_password.requestFocus();
              return;
          }
  
          mAuth.signInWithEmailAndPassword(email, password).addOnCompleteListener(LoginActivity.this, new OnCompleteListener&lt;AuthResult&gt;() {
              @Override
              public void onComplete(@NonNull Task&lt;AuthResult&gt; task) {
                  if (task.isSuccessful()) {
                      finish();
                      Intent intent = new Intent(LoginActivity.this, LoggedInActivity.class);
                      intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                      startActivity(intent);
                  } else {
                      Toast.makeText(getApplicationContext(), task.getException().getMessage(), Toast.LENGTH_SHORT).show();
                  }
              }
          });
      }
  
      @Override
      protected void onStart() {
          super.onStart();
  
          if (mAuth.getCurrentUser() != null) {
              finish();
              startActivity(new Intent(this, LoggedInActivity.class));
          }
      }
  
      @Override
      public void onClick(View view) {
          switch (view.getId()) {
              case R.id.register_tv:
                  finish();
                  Log.d("LoSeSANO", "Register Button Clicked");
                  startActivity(new Intent(LoginActivity.this, SignupActivity.class));
                  break;
  
              case R.id.login_button:
                  Log.d("LoSeSANO", "Login Button Clicked");
                  userLogin();
                  break;
          }
      }
  }
  </code></pre>
  
  <p>Here is the SignupActivity code</p>
  
  <pre><code>package com.mad.losesano;
  
  import android.app.Activity;
  import android.content.Intent;
  import android.os.Bundle;
  import android.support.annotation.NonNull;
  import android.util.Log;
  import android.util.Patterns;
  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.FirebaseAuthUserCollisionException;
  
  /**
   * Created by oshau on 01/03/2018.
   */
  
  public class SignupActivity extends Activity implements View.OnClickListener {
  
      EditText et_email, et_password;
      Button register_button;
      private FirebaseAuth mAuth;
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_signup);
  
          et_email = (EditText) findViewById(R.id.email_et_login);
          et_password = (EditText) findViewById(R.id.password_et_login);
  
          mAuth = FirebaseAuth.getInstance();
  
          register_button = (Button) findViewById(R.id.register_button);
          register_button.setOnClickListener(this);
          findViewById(R.id.login_tv).setOnClickListener(this);
  
      }
  
      private void registerUser() {
          Log.d("LoSeSANO", "Email Address: " + et_email.getText().toString());
          String email = et_email.getText().toString().trim();
          String password = et_password.getText().toString().trim();
  
          if (email.isEmpty()) {
              et_email.setError("Email is required");
              et_email.requestFocus();
              return;
          }
  
          if (!Patterns.EMAIL_ADDRESS.matcher(email).matches()) {
              et_email.setError("Please enter a valid email");
              et_email.requestFocus();
              return;
          }
  
          if (password.isEmpty()) {
              et_password.setError("Password is required");
              et_password.requestFocus();
              return;
          }
  
          if (password.length() &lt; 6) {
              et_password.setError("Minimum lenght of password should be 6");
              et_password.requestFocus();
              return;
          }
  
          mAuth.createUserWithEmailAndPassword(email, password).addOnCompleteListener(SignupActivity.this, new OnCompleteListener&lt;AuthResult&gt;() {
              @Override
              public void onComplete(@NonNull Task&lt;AuthResult&gt; task) {
                  if (task.isSuccessful()) {
                      finish();
                      startActivity(new Intent(SignupActivity.this, LoginActivity.class));
                  } else {
  
                      if (task.getException() instanceof FirebaseAuthUserCollisionException) {
                          Toast.makeText(getApplicationContext(), "You are already registered", Toast.LENGTH_SHORT).show();
  
                      } else {
                          Toast.makeText(getApplicationContext(), task.getException().getMessage(), Toast.LENGTH_SHORT).show();
                      }
  
                  }
              }
          });
  
      }
  
      @Override
      public void onClick(View view) {
          switch (view.getId()) {
              case R.id.register_button:
                  registerUser();
                  break;
  
              case R.id.login_tv:
                  finish();
                  startActivity(new Intent(SignupActivity.this, LoginActivity.class));
                  break;
          }
      }
  }
  </code></pre>
  
  <p>Here is my login_activity.xml and signup_activity.xml if needed</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;android.support.constraint.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"
      &gt;
  
      &lt;TextView
          android:id="@+id/welcome_tv"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:fontFamily="sans-serif-light"
          android:text="@string/welcome_string"
          android:textColor="#f0eeec"
          android:textSize="40dp"
          app:layout_constraintLeft_toLeftOf="parent"
          app:layout_constraintRight_toRightOf="parent"
          tools:layout_editor_absoluteY="80dp" /&gt;
  
      &lt;TextView
          android:id="@+id/textView2"
          android:layout_width="202dp"
          android:layout_height="62dp"
          android:layout_marginTop="8dp"
          android:fontFamily="sans-serif-light"
          android:gravity="center"
          android:text="@string/sub_welcome_string"
          android:textColor="#f0eeec"
          android:textSize="14dp"
          app:layout_constraintEnd_toEndOf="parent"
          app:layout_constraintLeft_toLeftOf="parent"
          app:layout_constraintTop_toBottomOf="@+id/welcome_tv" /&gt;
  
      &lt;EditText
          android:id="@+id/email_et_login"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_marginTop="8dp"
          android:backgroundTint="@android:color/holo_green_light"
          android:ems="10"
          android:fontFamily="sans-serif-light"
          android:inputType="textPersonName"
          android:text="@string/register_et_string"
          android:textColor="#f0eeec"
          app:layout_constraintHorizontal_bias="0.502"
          app:layout_constraintLeft_toLeftOf="parent"
          app:layout_constraintRight_toRightOf="parent"
          app:layout_constraintTop_toBottomOf="@+id/textView2" /&gt;
  
      &lt;EditText
          android:id="@+id/password_et_login"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_marginTop="8dp"
          android:backgroundTint="@android:color/holo_green_light"
          android:ems="10"
          android:fontFamily="sans-serif-light"
          android:hint="Password"
          android:inputType="textPassword"
          android:text="Password"
          android:textColor="#f0eeec"
          app:layout_constraintHorizontal_bias="0.502"
          app:layout_constraintLeft_toLeftOf="parent"
          app:layout_constraintRight_toRightOf="parent"
          app:layout_constraintTop_toBottomOf="@+id/email_et_login" /&gt;
  
      &lt;Button
          android:id="@+id/login_button"
          android:layout_width="151dp"
          android:layout_height="55dp"
          android:layout_marginTop="16dp"
          android:backgroundTint="#6c8c0e"
          android:fontFamily="sans-serif-light"
          android:text="@string/login_register_button_string"
          android:textColor="#f0eeec"
          app:layout_constraintHorizontal_bias="0.502"
          app:layout_constraintLeft_toLeftOf="parent"
          app:layout_constraintRight_toRightOf="parent"
          app:layout_constraintTop_toBottomOf="@+id/password_et_login" /&gt;
  
      &lt;TextView
          android:id="@+id/register_tv"
          android:layout_width="wrap_content"
          android:layout_height="22dp"
          android:layout_marginTop="8dp"
          android:backgroundTint="#6c8c0e"
          android:fontFamily="sans-serif-light"
          android:text="@string/register_tv_string"
          android:textColor="#f0eeec"
          android:textSize="16dp"
          app:layout_constraintLeft_toLeftOf="parent"
          app:layout_constraintRight_toRightOf="parent"
          app:layout_constraintTop_toBottomOf="@+id/login_button" /&gt;
  
      &lt;TextView
          android:id="@+id/password_tv"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_marginTop="20dp"
          android:backgroundTint="#6c8c0e"
          android:fontFamily="sans-serif-light"
          android:text="@string/forgot_password_tv_string"
          android:textColor="#f0eeec"
          android:textSize="16dp"
          app:layout_constraintHorizontal_bias="0.501"
          app:layout_constraintLeft_toLeftOf="parent"
          app:layout_constraintRight_toRightOf="parent"
          app:layout_constraintTop_toBottomOf="@+id/register_tv" /&gt;
  
  &lt;/android.support.constraint.ConstraintLayout&gt;
  </code></pre>
  
  <p>signup_activity</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;android.support.constraint.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"
      &gt;
  
      &lt;TextView
          android:id="@+id/welcome_tv"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:fontFamily="sans-serif-light"
          android:text="@string/welcome_string"
          android:textColor="#f0eeec"
          android:textSize="40dp"
          app:layout_constraintLeft_toLeftOf="parent"
          app:layout_constraintRight_toRightOf="parent"
          tools:layout_editor_absoluteY="80dp" /&gt;
  
      &lt;TextView
          android:id="@+id/textView2"
          android:layout_width="202dp"
          android:layout_height="62dp"
          android:layout_marginTop="8dp"
          android:fontFamily="sans-serif-light"
          android:gravity="center"
          android:text="@string/sub_welcome_string"
          android:textColor="#f0eeec"
          android:textSize="14dp"
          app:layout_constraintEnd_toEndOf="parent"
          app:layout_constraintLeft_toLeftOf="parent"
          app:layout_constraintTop_toBottomOf="@+id/welcome_tv" /&gt;
  
      &lt;EditText
          android:id="@+id/email_et_login"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_marginTop="8dp"
          android:backgroundTint="@android:color/holo_green_light"
          android:ems="10"
          android:fontFamily="sans-serif-light"
          android:inputType="textPersonName"
          android:text="@string/register_et_string"
          android:textColor="#f0eeec"
          app:layout_constraintHorizontal_bias="0.502"
          app:layout_constraintLeft_toLeftOf="parent"
          app:layout_constraintRight_toRightOf="parent"
          app:layout_constraintTop_toBottomOf="@+id/textView2" /&gt;
  
      &lt;EditText
          android:id="@+id/password_et_login"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_marginTop="8dp"
          android:backgroundTint="@android:color/holo_green_light"
          android:ems="10"
          android:fontFamily="sans-serif-light"
          android:hint="Password"
          android:inputType="textPassword"
          android:text="Password"
          android:textColor="#f0eeec"
          app:layout_constraintHorizontal_bias="0.502"
          app:layout_constraintLeft_toLeftOf="parent"
          app:layout_constraintRight_toRightOf="parent"
          app:layout_constraintTop_toBottomOf="@+id/email_et_login" /&gt;
  
      &lt;Button
          android:id="@+id/register_button"
          android:layout_width="151dp"
          android:layout_height="55dp"
          android:layout_marginTop="16dp"
          android:backgroundTint="#6c8c0e"
          android:fontFamily="sans-serif-light"
          android:text="@string/register_tv_string"
          android:textColor="#f0eeec"
          app:layout_constraintHorizontal_bias="0.502"
          app:layout_constraintLeft_toLeftOf="parent"
          app:layout_constraintRight_toRightOf="parent"
          app:layout_constraintTop_toBottomOf="@+id/password_et_login" /&gt;
  
      &lt;TextView
          android:id="@+id/login_tv"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_marginTop="12dp"
          android:backgroundTint="#6c8c0e"
          android:fontFamily="sans-serif-light"
          android:text="@string/login_register_button_string"
          android:textColor="#f0eeec"
          android:textSize="16dp"
          app:layout_constraintLeft_toLeftOf="parent"
          app:layout_constraintRight_toRightOf="parent"
          app:layout_constraintTop_toBottomOf="@+id/register_button" /&gt;
  
  &lt;/android.support.constraint.ConstraintLayout&gt;
  </code></pre>
  
  <p>Any help would be greatly appreciated!</p>