title: classifier does not have a companion object
body: <p>i want to use BottomNavigationView in my app and i'm facing this problem with kotlin (never had it before with java) i see this message :
  classifier 'listFragment' does not have a companion object and thus must be initialized here</p>
  
  <p>this is my code :</p>
  
  <pre><code>private val mOnNavigationItemSelectedListener = BottomNavigationView.OnNavigationItemSelectedListener { item -&gt;
      when (item.itemId) {
          R.id.listNav -&gt; {
  //the problem is here in listFragment word below
              setFragment(listFragment)
              return@OnNavigationItemSelectedListener true
          }
          R.id.accountNav -&gt; {
  //the problem is here also in accountFragment word below
              setFragment(accountFragment)
              return@OnNavigationItemSelectedListener true
          }
  false 
  }
  private fun setFragment(fragment: Fragment) {
      supportFragmentManager.beginTransaction().replace(R.id.mainFrame , fragment).commit()
  }
  </code></pre>
  
  <p>any help is appreciated :) </p>