How to avoid NullPointerException on orientation change in application with FragmentTabHost?

Question

Android

I have an application that I developed for a long time and initially turned off the orientation change - left only portrait.
Over time, the application has grown and now, when I want to make it work in both portrait and landscape orientations, a java.lang.NullPointerException
error pops up. located on this layout.
I must say that this is one of the 4 layouts that are in FragmentTabHost.
And when defining the button, there is no error.

helpBtn = (Button) rootView.findViewById(R.id.helpBtn);

it comes when any of its properties are changed, for example:
helpBtn.setVisibility(View.GONE);
It must be said that this is one of 4 layouts and each of them is in FragmentTabHost

android:configChanges="orientation|keyboardHidden|screenSize"

android:configChanges tried different ones, always when switching FragmentTabHost to this layout in landscape orientation, a java.lang.NullPointerException occurs on changing the properties of this button
helpBtn.setVisibility(View.GONE);
. Moreover, in this layout there are other buttons and controls on them, no error occurs, but on this and another two - arises.
Please help me figure it out.
I'm ready to receive the answer privately, and then post it here.