Could someone explain to me why this null pointer exception?

Logcat

  

java.lang.NullPointerException: Attempt to invoke virtual method   'android.text.Editable android.widget.EditText.getText ()' on a null   object reference                                                                                         at   com.paivadeveloper.megamessenger.RegisterActivity $ 1.onClick (RegisterActivity.java:49)                                                                                         at android.view.View.performClick (View.java:6261)                                                                                         at android.widget.TextView.performClick (TextView.java:11159)                                                                                         at android.view.View $ PerformClick.run (View.java:23748)                                                                                         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:6776)                                                                                         at java.lang.reflect.Method.invoke (Native Method)                                                                                         at   com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run (ZygoteInit.java:1496)                                                                                         at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1386)

Java

public class RegisterActivity extends AppCompatActivity {
private FirebaseAuth mAuth;


private TextInputLayout mDisplayName;
private TextInputLayout mEmail;
private TextInputLayout mPassword;
private Button mCreateBtn;

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

    mAuth = FirebaseAuth.getInstance();

    mDisplayName = (TextInputLayout) findViewById(R.id.reg_display_name);
    mEmail = (TextInputLayout) findViewById(R.id.reg_email);
    mPassword = (TextInputLayout) findViewById(R.id.reg_password);
    mCreateBtn = (Button) findViewById(R.id.reg_create_btn);


    mCreateBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            String display_name = mDisplayName.getEditText().getText().toString();
            String email = mEmail.getEditText().getText().toString();
            String password = mPassword.getEditText().getText().toString();

            register_user(display_name, email, password);
        }
    });

}

private void register_user(String display_name, String email, String password) {

    mAuth.createUserWithEmailAndPassword(email, password).addOnCompleteListener(new OnCompleteListener<AuthResult>() {
        @Override
        public void onComplete(@NonNull Task<AuthResult> task) {
            if (task.isSuccessful()) {
                Intent mainIntent = new Intent(RegisterActivity.this, MainActivity.class);
                startActivity(mainIntent);
                finish();
            } else {
                Toast.makeText(RegisterActivity.this, "Erro , contate-nos", Toast.LENGTH_LONG).show();
            }
        }
    });
    }

    }

Thank you