ArgumentCaptor capture returning null

I have a situation where I need to test one object which is created inside public method and I don't have access to it so I am trying to use ArgumentCaptor. The problem is I'm always getting null.

Here is my code so it would be maybe more visible what I'm doing wrong:

class ActivityStarterClass(val c: Context) {

    public void startActivity() {
       val intent = createSomeIntent()
       c.startActivity(intent)
    }
}

class ActivityStarterClassTest() {
  val c = mock<Context>()

  @Test
  fun testActivityStart() {
    val activityStarter = ActivityStarterClass(c)
    argumentCaptor<Intent>().apply {
        verify(context).startActivity(capture())
        System.out.println("captured intent: " + firstValue)
    }
  }
}