Error wanting to enter the App

The Logcat throws me this error

E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.example.matias.finalcode, PID: 9952
                  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.example.matias.finalcode.LoginActivity$3.onClick(LoginActivity.java:91)
                      at android.view.View.performClick(View.java:4757)
                      at android.view.View$PerformClick.run(View.java:19757)
                      at android.os.Handler.handleCallback(Handler.java:739)
                      at android.os.Handler.dispatchMessage(Handler.java:95)
                      at android.os.Looper.loop(Looper.java:135)
                      at android.app.ActivityThread.main(ActivityThread.java:5258)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at java.lang.reflect.Method.invoke(Method.java:372)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:898)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693)
I/Process: Sending signal. PID: 9952 SIG: 9
Application terminated.

And this is the code that gives an error according to the Logcat ...

auth.signInWithEmailAndPassword(email, password)
                        .addOnCompleteListener(LoginActivity.this, new OnCompleteListener<AuthResult>() {
                            @Override
                            public void onComplete(@NonNull Task<AuthResult> task) {
                                // If sign in fails, display a message to the user. If sign in succeeds
                                // the auth state listener will be notified and logic to handle the
                                // signed in user can be handled in the listener.
                                progressBar.setVisibility(View.GONE);
                                if (!task.isSuccessful()) {
                                    // there was an error
                                    if (password.length() < 6) {
                                        inputPassword.setError(getString(R.string.minimum_password));
                                    } else {
                                        Toast.makeText(LoginActivity.this, getString(R.string.auth_failed), Toast.LENGTH_LONG).show();
                                    }
                                } else {
                                    Intent intent = new Intent(LoginActivity.this, InicioActivity.class);
                                    //Intent intent = new Intent(LoginActivity.this, LookingService.class);
                                    startActivity(intent);
                                    finish();
                            }
                        }
            });

What can it be? ...

Thank you very much for your time, I hope you can help me. Greetings!