无法启动活动组件信息{e\u homes.app.com.e\u homes/e\u homes.app.com.e\u homes.location}:java.lang.nullpointerexception。这个错误出现在我的代码中。我使用了firebase身份验证，但是当我登录时，它给出了上面的错误。这是密码

public class MainActivity extends AppCompatActivity {
private FirebaseAuth fb;
private ProgressDialog progressDialog;
private FirebaseAuth.AuthStateListener mAuthListener;
Button txtRegister;
EditText etEmail,etPassword;
Button Register;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    fb = FirebaseAuth.getInstance();
    txtRegister = (Button) findViewById(R.id.signup);
    etEmail = (EditText) findViewById(R.id.username);
    etPassword = (EditText) findViewById(R.id.password);
    Register = (Button) findViewById(R.id.signin);
    progressDialog = new ProgressDialog(this);
    mAuthListener=new FirebaseAuth.AuthStateListener() {
        @Override
        public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
            if(firebaseAuth.getCurrentUser()!=null) {
                startActivity(new Intent(getApplicationContext(), 
 Location.class));
            }

        }
    };

    Register.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            userLogin();
        }
    });
    txtRegister.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v)
        {
            Intent intent = new 
 Intent(MainActivity.this,Registration.class);
            startActivity(intent);
        }
    });
 }

  @Override
  protected void onStart() {
    fb.addAuthStateListener(mAuthListener);
    super.onStart();
  }

  private void userLogin() {
    String email_id = etEmail.getText().toString().trim();
    String password = etPassword.getText().toString().trim();
    if (TextUtils.isEmpty(email_id)) {
        Toast.makeText(this, "please enter your Email_Id", 
Toast.LENGTH_SHORT).show();
        return;
    } else if (TextUtils.isEmpty(password)) {
        Toast.makeText(this, "please enter your password", 
Toast.LENGTH_SHORT).show();
        return;
    } else {
        progressDialog.setMessage("Logining in....Please wait....");
        progressDialog.show();
        fb.signInWithEmailAndPassword(email_id, password).
                addOnCompleteListener(this, new 
 OnCompleteListener<AuthResult>() {
                    @Override
                    public void onComplete(@NonNull Task<AuthResult> task) {
                        progressDialog.dismiss();
                        if (task.isSuccessful()) {
                          //  startActivity(new 
 Intent(getApplicationContext(), Location.class));
                         //   finish();
                        } else {
                            Toast.makeText(MainActivity.this, "Invalid email 
 Id or password", Toast.LENGTH_SHORT).show();
                        }
                    }
                });
    }
  }

}

整个错误是：

FATAL EXCEPTION: main

    Process: e_homes.app.com.e_homes, PID: 7302
   java.lang.RuntimeException: Unable to start activity ComponentInfo{e_homes.app.com.e_homes/e_homes.app.com.e_homes.Location}: java.lang.NullPointerException
       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2338)
       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390)
       at android.app.ActivityThread.access$800(ActivityThread.java:151)
       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
       at android.os.Handler.dispatchMessage(Handler.java:110)
       at android.os.Looper.loop(Looper.java:193)
       at android.app.ActivityThread.main(ActivityThread.java:5299)
       at java.lang.reflect.Method.invokeNative(Native Method)
       at java.lang.reflect.Method.invoke(Method.java:515)
       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:829)
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:645)
       at dalvik.system.NativeStart.main(Native Method)
    Caused by: java.lang.NullPointerException
       at e_homes.app.com.e_homes.Location.onCreate(Location.java:31)
       at android.app.Activity.performCreate(Activity.java:5264)
       at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1088)
       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2302)
       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390) 
       at android.app.ActivityThread.access$800(ActivityThread.java:151) 
       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321) 
       at android.os.Handler.dispatchMessage(Handler.java:110) 
       at android.os.Looper.loop(Looper.java:193) 
       at android.app.ActivityThread.main(ActivityThread.java:5299) 
       at java.lang.reflect.Method.invokeNative(Native Method)