Process: com.example.vicevirus.myapplication, PID: 13471
java.lang.NullPointerException: Attempt to invoke virtual method ‘java.lang.String com.google.firebase.auth.FirebaseUser.getUid()’ on a null object reference
at com.example.vicevirus.myapplication.RegisterActivity$1.onComplete(RegisterActivity.java:48)
at com.google.android.gms.tasks.zzc$1.run(Unknown Source)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

这是在android显示器上。我该如何解决？

package com.example.vicevirus.myapplication;

import android.app.ProgressDialog;
         import android.support.annotation.NonNull;
         import android.support.v7.app.AppCompatActivity;
         import android.os.Bundle;
         import android.view.View;
         import android.widget.EditText;
         import android.widget.Toast;
         import com.google.android.gms.tasks.OnCompleteListener;
         import com.google.android.gms.tasks.OnSuccessListener;
         import com.google.android.gms.tasks.Task;
         import com.google.firebase.auth.AuthResult;
         import com.google.firebase.auth.FirebaseAuth;
         import com.google.firebase.database.DatabaseReference;
         import com.google.firebase.database.FirebaseDatabase;

public class RegisterActivity extends AppCompatActivity {
    private EditText email,name,password;
    DatabaseReference databaseReference;
    FirebaseAuth mAuth;
    private DatabaseReference userIdRef;
    ProgressDialog registerDialog;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_register);
        email=(EditText)findViewById(R.id.email);
        name=(EditText)findViewById(R.id.name);
        password=(EditText)findViewById(R.id.password);
        databaseReference= FirebaseDatabase.getInstance().getReference().child("chat_users");
        mAuth=FirebaseAuth.getInstance();
        registerDialog=new ProgressDialog(this);
        registerDialog.setMessage("Registering..");
    }
    public void submit(View view) {
        registerDialog.show();
        mAuth.createUserWithEmailAndPassword(email.getText().toString(),password.getText().toString()).addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
            @Override
            public void onComplete(@NonNull Task<AuthResult> task) {
                if(task.isComplete())
                {
                    registerDialog.dismiss();
                    Toast.makeText(getApplicationContext(),"Registered successfully",Toast.LENGTH_SHORT).show();
                    userIdRef=databaseReference.child(mAuth.getCurrentUser().getUid());
                    userIdRef.child("name").setValue(name.getText().toString());
                    finish();
                }
                registerDialog.dismiss();
            }
        });
    }
}