SignUpActivity crashing Ribbit application

Whats up guys, it seems I'm having a problem with my SignUpActivity class. I compared my class code with the code provided in the file download, and they're identical (with exception of a few string resource names). My logcat is telling me that I have a null pointer exception in my on click listener, specifically line 41. This is the

String username = mUsername.getText().toString();

The rest of the error code is as follows:

Process: com.example.nicholas.ribbit, PID: 1596 java.lang.NullPointerException at com.example.nicholas.ribbit.SignUpActivity$1.onClick(SignUpActivity.java:41) at android.view.View.performClick(View.java:4438) at android.view.View$PerformClick.run(View.java:18422) at android.os.Handler.handleCallback(Handler.java:733) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:136) at android.app.ActivityThread.main(ActivityThread.java:5017) 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:779) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) at dalvik.system.NativeStart.main(Native Method)

I've been trying to figure this out for the past few hours to no avail, and since I'm up to relating users via parse, I can't really ignore this any longer. Any help would be greatly appreciated