Stuck on "Error Messages with Dialogs" video in the ribbit app. Please help!

Hello,

I am building the ribbit app and I am on the "Error Messages with Dialogs" video. My code is not showing any errors and when I run the app it starts. However, when I click on the "Sign Up" label to go to the Sign Up Activity to text my error message dialog the app crashes. The error on the emulator I get is "Unfortunately, Ribbit has stopped."

in LogCat I see the following errors:

06-04 04:14:18.578: E/AndroidRuntime(1469): FATAL EXCEPTION: main 06-04 04:14:18.578: E/AndroidRuntime(1469): Process: com.erinkabbash.ribbit, PID: 1469 06-04 04:14:18.578: E/AndroidRuntime(1469): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.erinkabbash.ribbit/com.erinkabbash.ribbit.SignUpActivity}: java.lang.NullPointerException 06-04 04:14:18.578: E/AndroidRuntime(1469): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195) 06-04 04:14:18.578: E/AndroidRuntime(1469): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245) 06-04 04:14:18.578: E/AndroidRuntime(1469): at android.app.ActivityThread.access$800(ActivityThread.java:135) 06-04 04:14:18.578: E/AndroidRuntime(1469): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196) 06-04 04:14:18.578: E/AndroidRuntime(1469): at android.os.Handler.dispatchMessage(Handler.java:102) 06-04 04:14:18.578: E/AndroidRuntime(1469): at android.os.Looper.loop(Looper.java:136) 06-04 04:14:18.578: E/AndroidRuntime(1469): at android.app.ActivityThread.main(ActivityThread.java:5017) 06-04 04:14:18.578: E/AndroidRuntime(1469): at java.lang.reflect.Method.invokeNative(Native Method) 06-04 04:14:18.578: E/AndroidRuntime(1469): at java.lang.reflect.Method.invoke(Method.java:515) 06-04 04:14:18.578: E/AndroidRuntime(1469): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 06-04 04:14:18.578: E/AndroidRuntime(1469): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 06-04 04:14:18.578: E/AndroidRuntime(1469): at dalvik.system.NativeStart.main(Native Method) 06-04 04:14:18.578: E/AndroidRuntime(1469): Caused by: java.lang.NullPointerException 06-04 04:14:18.578: E/AndroidRuntime(1469): at com.erinkabbash.ribbit.SignUpActivity.onCreate(SignUpActivity.java:28) 06-04 04:14:18.578: E/AndroidRuntime(1469): at android.app.Activity.performCreate(Activity.java:5231) 06-04 04:14:18.578: E/AndroidRuntime(1469): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087) 06-04 04:14:18.578: E/AndroidRuntime(1469): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159) 06-04 04:14:18.578: E/AndroidRuntime(1469): ... 11 more

The code in my SignUpActivity.java is:

package com.erinkabbash.ribbit;

import android.app.Activity;
import android.app.AlertDialog;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class SignUpActivity extends Activity {

    protected EditText mUsername;
    protected EditText mPassword;
    protected EditText mEmail;
    protected Button mSignUpButton;

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

        mUsername = (EditText) findViewById(R.id.usernameField);
        mPassword = (EditText) findViewById(R.id.passwordField);
        mEmail = (EditText) findViewById(R.id.emailField);
        mSignUpButton = (Button) findViewById(R.id.signUpButton);
        mSignUpButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String username = mUsername.getText().toString();
                String password = mPassword.getText().toString();
                String email = mEmail.getText().toString();

                username = username.trim();
                password = password.trim();
                email = email.trim();

                if (username.isEmpty() || password.isEmpty() || email.isEmpty()) {
                    AlertDialog.Builder builder = new AlertDialog.Builder(SignUpActivity.this);
                    builder.setMessage(R.string.sign_up_error_message)
                        .setTitle(R.string.sign_up_error_title)
                        .setPositiveButton(android.R.string.ok, null);

                    AlertDialog dialog = builder.create();
                    dialog.show();
                }else {
                    //create the new user
                }                   
            }
        });

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.sign_up, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

Any ideas what I am missing? I cannot seem to figure out what is crashing the app.

Thanks in advanced for any help you can provide!

Sincerely,

Erin S Kabbash