exitFreeformMode: You can only go fullscreen from freeform

Question

when we run this code app is crashing and if I remove this code app work without any problem why this is happening? what is wrong here?

 mAuth=FirebaseAuth.getInstance();
    //_FirebaseImageUploader m_FirebaseImageUploader;
    if(mAuth!=null?mAuth.getCurrentUser()!=null?true:false:false){

    }
    else{
        List<AuthUI.IdpConfig> providers = Arrays.asList(
                new AuthUI.IdpConfig.EmailBuilder().build(),
                new AuthUI.IdpConfig.PhoneBuilder().build(),
                new AuthUI.IdpConfig.GoogleBuilder().build());// Create and launch sign-in intent
        startActivityForResult(
                AuthUI.getInstance()
                        .createSignInIntentBuilder()
                        .setAvailableProviders(providers)
                        .build(),
                RC_SIGN_IN);
    }