public void signup() {
    Log.d(TAG, "Signup");

    if (!validate()) {
        onSignupFailed();
        return;
    }


    final ProgressDialog progressDialog = new ProgressDialog(SignupActivity.this,
            R.style.AppTheme_Dark_Dialog);
    progressDialog.setIndeterminate(true);
    progressDialog.setMessage("Creating Account...");
    progressDialog.show();

    mNewFirebaseUserEmail = _emailText.getText().toString();
    mNewFirebaseUserPassword = _passwordText.getText().toString();

    new Handler().postDelayed(
            new Runnable() {
                public void run() {
                    // On complete call either onSignupSuccess or onSignupFailed
                    // depending on success
                    onSignupSuccess();
                    // onSignupFailed();
                    progressDialog.dismiss();
                }
            }, 3000);
    onSignupSuccess();
}

public void onSignupSuccess() {
    signupButton.setEnabled(true);
    //not sure why this line is here
    setResult(RESULT_OK, null);
    //this line below actually creates the user in Firebase; does not write or save to any locations
    mAuth.createUserWithEmailAndPassword(mNewFirebaseUserEmail, mNewFirebaseUserPassword)
            .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                @Override
                public void onComplete(@NonNull Task<AuthResult> task) {
                    Log.d(TAG, "signInWithEmail:onComplete:" + task.isSuccessful());
                    FirebaseAuth loggedInAuth = FirebaseAuth.getInstance();
                    NULL BEING THROWN HERE
                    String ID = loggedInAuth.getCurrentUser().getUid();
                    //TODO: Update handling of display name
                    String displayName = mAuth.getCurrentUser().getUid();
                    HashMap<String, Object> id = new HashMap<>();
                    id.put("user_id", ID);
                    id.put("display_name", displayName);
                    mUserRef.child(ID).updateChildren(id);

                    // If sign in fails, display a message to the user. If sign in succeeds
                    // the auth state listener will be notified and logic to handle the
                    // signed in user can be handled in the listener.
                    if (!task.isSuccessful()) {
                        Log.w(TAG, "signInWithEmail:failed", task.getException());
                        Toast.makeText(SignupActivity.this, "Authentication Failed with Email",
                                Toast.LENGTH_SHORT).show();
                    }
                }
            });
}

09-28 21:00:08.822 6591-6591/com.troychuinard.fanpolls E/AndroidRuntime: FATAL EXCEPTION: main
                                                                     Process: com.troychuinard.fanpolls, PID: 6591
                                                                     java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.google.firebase.auth.FirebaseUser.getUid()' on a null object reference
                                                                         at com.troychuinard.fanpolls.SignupActivity$5.onComplete(SignupActivity.java:279)
                                                                         at com.google.android.gms.tasks.zzc$1.run(Unknown Source)
                                                                         at android.os.Handler.handleCallback(Handler.java:739)
                                                                         at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                         at android.os.Looper.loop(Looper.java:148)
                                                                         at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                                         at java.lang.reflect.Method.invoke(Native Method)
                                                                         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

mAuth.createUserWithEmailAndPassword(mNewFirebaseUserEmail, mNewFirebaseUserPassword)
            .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                @Override
                public void onComplete(@NonNull Task<AuthResult> task) {
                    if (task.isSuccessful()) {
                        // Sign in success, update UI with the signed-in user's information
                        Log.d(TAG, "createUserWithEmail:success");
                        FirebaseUser user = mAuth.getCurrentUser();
                        Log.d(TAG, "user:"+user.getUid());
                    } else {
                        // If sign in fails, display a message to the user.
                        Log.w(TAG, "createUserWithEmail:failure", task.getException());
                        Toast.makeText(EmailPasswordActivity.this, "Authentication failed.",
                                Toast.LENGTH_SHORT).show();
                    }

                }
            });