java.lang.NullPointerException: Attempt to invoke virtual methodをなくしたい

**【目標】
ncmb(nifty cloud mobile backend)とkotlinでログイン機能の実装

【経緯】
githubにあるjavaファイルをkotlinに変更して進めているところです。
該当ファイルのあるURL↓
https://github.com/NIFCloud-mbaas/android_login_demo

【問題とお願い】
・アプリはクラッシュしないのですが、常にerrorがあることで、サーバーにアカウントを作成することができない?
・下記コードのlogcatエラーをなくしたいので、アドバイス願います、、、

【コード】**

logcat（問題発生時）

07-06 21:02:32.838 2225-2302/? E/WindowManager: Unhandled exception in Window Manager
    java.lang.NullPointerException: Attempt to invoke virtual method 'void com.android.server.wm.DisplayContent.getLogicalDisplayRect(android.graphics.Rect)' on a null object reference
        at com.android.server.wm.WindowState.computeFrameLw(WindowState.java:882)
        at com.android.server.policy.PhoneWindowManager.layoutWindowLw(PhoneWindowManager.java:5044)
        at com.android.server.wm.WindowSurfacePlacer.performLayoutLockedInner(WindowSurfacePlacer.java:1007)
        at com.android.server.wm.WindowSurfacePlacer.applySurfaceChangesTransaction(WindowSurfacePlacer.java:664)
        at com.android.server.wm.WindowSurfacePlacer.performSurfacePlacementInner(WindowSurfacePlacer.java:322)
        at com.android.server.wm.WindowSurfacePlacer.performSurfacePlacementLoop(WindowSurfacePlacer.java:235)
        at com.android.server.wm.WindowSurfacePlacer.performSurfacePlacement(WindowSurfacePlacer.java:183)
        at com.android.server.wm.WindowManagerService.relayoutWindow(WindowManagerService.java:3128)
        at com.android.server.wm.Session.relayout(Session.java:227)
        at android.view.ViewRootImpl.relayoutWindow(ViewRootImpl.java:6202)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2012)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1462)
        at android.view.WindowManagerGlobal.doTraversal(WindowManagerGlobal.java:394)
        at com.android.server.policy.PhoneWindowManager.addFastStartingWindow(PhoneWindowManager.java:8490)
        at com.android.server.wm.WindowManagerService$H.handleMessage(WindowManagerService.java:8402)
        at android.os.Handler.dispatchMessage(Handler.java:110)
        at android.os.Looper.loop(Looper.java:203)
        at android.os.HandlerThread.run(HandlerThread.java:61)
        at com.android.server.ServiceThread.run(ServiceThread.java:46)

SignupActivity（問題activity）

@file:Suppress("DEPRECATION")

package com.nifty.user

import android.app.Activity
import android.app.ProgressDialog
import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import android.util.Log
import android.widget.Toast

import com.nifty.cloud.mb.core.NCMBUser

import kotlinx.android.synthetic.main.activity_signup.*
import org.jetbrains.anko.startActivity

@Suppress("DEPRECATION")
class SignupActivity : AppCompatActivity() {


    public override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_signup)

        btn_signup!!.setOnClickListener { signup() }

        link_login!!.setOnClickListener {
            // Finish the registration screen and return to the Login activity
            startActivity<LoginActivity>()
        }
    }

    private fun signup() {
        Log.d(TAG, "Signup")

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

        btn_signup!!.isEnabled = false

        val progressDialog = ProgressDialog(this@SignupActivity,
                R.style.AppTheme_Dark_Dialog)
        progressDialog.isIndeterminate = true
        progressDialog.setMessage("Creating Account...")
        progressDialog.show()

        val name = input_name!!.text.toString()
        val password = input_password!!.text.toString()

        // TODO: Implement your own signup logic here.
        //NCMBUserのインスタンスを作成
        val user = NCMBUser()
        //ユーザ名を設定
        user.userName = name
        //パスワードを設定
        user.setPassword(password)
        //設定したユーザ名とパスワードで会員登録を行う

        user.signUpInBackground { e  ->
            if (e != null) {
                //会員登録時にエラーが発生した場合の処理
                onSignupFailed()
            } else {
                android.os.Handler().postDelayed(
                        {
                            // On complete call either onSignupSuccess or onSignupFailed
                            // depending on success
                            onSignupSuccess()
                            // onSignupFailed();
                            progressDialog.dismiss()
                        }, 3000)
            }
        }
    }


    private fun onSignupSuccess() {
        btn_signup!!.isEnabled = true
        setResult(Activity.RESULT_OK, null)
        finish()
    }

    private fun onSignupFailed() {
        Toast.makeText(baseContext, "Signup failed", Toast.LENGTH_LONG).show()

        btn_signup!!.isEnabled = true
    }

    private fun validate(): Boolean {
        var valid = true

        val name = input_name!!.text.toString()
        val password = input_password!!.text.toString()

        if (name.isEmpty() || name.length < 3) {
            input_name!!.error = "at least 3 characters"
            valid = false
        } else {
            input_name!!.error = null
        }

        if (password.isEmpty() || password.length < 4 || password.length > 10) {
            input_password!!.error = "between 4 and 10 alphanumeric characters"
            valid = false
        } else {
            input_password!!.error = null
        }

        return valid
    }

    companion object {
        private const val TAG = "SignupActivity"
    }
}

MainActivity(アプリケーションキー等記載)

package com.nifty.user

import android.content.Intent
import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import android.view.Menu
import android.view.MenuItem
import com.nifty.cloud.mb.core.NCMB
import com.nifty.cloud.mb.core.NCMBUser

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        //**************** APIキーの設定とSDKの初期化 **********************
        NCMB.initialize(this.applicationContext, "7e6d6479ddc9c642f4229d2041c4a6093d2d1f45385c350543523c9b4c328e4f",
                "c81eea502681d9c069ca4104b98420ff59318b07f76aeec1cca3c816bbf08e87")

        val intent = Intent(this, LoginActivity::class.java)
        startActivity(intent)
    }

    override fun onCreateOptionsMenu(menu: Menu): Boolean {
        // Inflate the menu; this adds items to the action bar if it is present.
        menuInflater.inflate(R.menu.menu_main, menu)
        return true
    }

    override fun onOptionsItemSelected(item: MenuItem): Boolean {
        // 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.
        val id = item.itemId


        if (id == R.id.action_settings) {
            return true
        }

        if (id == R.id.action_logout) {
            NCMBUser.logoutInBackground { e ->
                if (e != null) {
                    //エラー時の処理
                }
            }
            val intent = Intent(this, LoginActivity::class.java)
            startActivity(intent)
            return true
        }

        return super.onOptionsItemSelected(item)
    }
}

この問題に長い時間を取られております、、、
何卒、何卒、ご教授のほどよろしくお願いします！！！