title: FATAL EXCEPTION: main KotlinNullPointerException
body: <p>This is my first time building an android application. However when i run the app on my Virtual Device, it stopped working and keeps crashing. The error says something about null pointer exception. This is my first time using Kotlin and I coded in Java and changed to Kotlin.</p>
  
  <pre><code> override fun onCreate(savedInstanceState: Bundle?) {
      super.onCreate(savedInstanceState)
      setContentView(R.layout.activity_add_sales)
  
      val date: EditText? = null
      val changeDate: CheckBox? = null
      val yes: RadioButton? = null
      val no: RadioButton? = null
  
      date!!.setText("15-11-2017")
      date.isEnabled = false
  
      val button2 = findViewById&lt;View&gt;(R.id.btnSubmit) as Button
      button2.setOnClickListener {
          var name = findViewById&lt;View&gt;(R.id.name) as EditText
          var cost = findViewById&lt;View&gt;(R.id.cost) as EditText
          val itemcost = Integer.parseInt(cost!!.text.toString())
          var price = findViewById&lt;View&gt;(R.id.price) as EditText
          val itemprice = Integer.parseInt(price!!.text.toString())
          var qty = findViewById&lt;View&gt;(R.id.quantity) as EditText
          var chgDate = false
          var discount = false
          val toast = Toast(applicationContext)
          if (itemprice &lt; itemcost) {
              price!!.error = "Selling price cannot be lower than item price!"
          } else {
              if (changeDate!!.isChecked) {
                  chgDate = true
                  date.isEnabled = true
              }
              if (yes!!.isChecked) {
                  discount = true
              }
          }
          Toast.makeText(this@AddSales, "Item Name: " + name!!.text + "\n" + "Cost: " + cost!!.text + "\n" + "Item Price: " + price!!.text + "\n" + "Quantity: " + qty!!.text + "Date: " + date + "Staff Discount: " + discount, Toast.LENGTH_SHORT).show()
      }
  
  }
  </code></pre>
  
  <p>and the error is:</p>
  
  <blockquote>
    <p>11-17 06:23:34.603 3540-3540/com.example.ruiru.salestracker
    E/AndroidRuntime: FATAL EXCEPTION: main
                                                                                  Process: com.example.ruiru.salestracker, PID: 3540
                                                                                  java.lang.RuntimeException: Unable to start activity
    ComponentInfo{com.example.ruiru.salestracker/com.example.ruiru.salestracker.AddSales}:
    kotlin.KotlinNullPointerException
                                                                                      at
    android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817)
                                                                                      at
    android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
                                                                                      at android.app.ActivityThread.-wrap11(Unknown Source:0)
                                                                                      at
    android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
                                                                                      at android.os.Handler.dispatchMessage(Handler.java:105)
                                                                                      at android.os.Looper.loop(Looper.java:164)
                                                                                      at android.app.ActivityThread.main(ActivityThread.java:6541)
                                                                                      at java.lang.reflect.Method.invoke(Native Method)
                                                                                      at
    com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
                                                                                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
                                                                                   Caused by: kotlin.KotlinNullPointerException
                                                                                      at com.example.ruiru.salestracker.AddSales.onCreate(AddSales.kt:25)
                                                                                      at android.app.Activity.performCreate(Activity.java:6975)
                                                                                      at
    android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1213)
                                                                                      at
    android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2770)
                                                                                      at
    android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892) 
                                                                                      at android.app.ActivityThread.-wrap11(Unknown Source:0) 
                                                                                      at
    android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593) 
                                                                                      at android.os.Handler.dispatchMessage(Handler.java:105) 
                                                                                      at android.os.Looper.loop(Looper.java:164) 
                                                                                      at android.app.ActivityThread.main(ActivityThread.java:6541) 
                                                                                      at java.lang.reflect.Method.invoke(Native Method) 
                                                                                      at
    com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 
                                                                                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)</p>
  </blockquote>