How to set default state to EXPANDED

[marekbil]

I call in onCreate() in activity

slidingPanel.slideTo(PanelState.EXPANDED);

but it error:
java.lang.RuntimeException: Unable to start activity ComponentInfo{pl.novitus.bill/pl.novitus.bill.ui.sale.SaleActivity}: kotlin.UninitializedPropertyAccessException: lateinit property slidingView has not been initialized
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2666)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2727)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1478)