private Set < String > getNotNullExtraKeys ( Node actual , Set < String > extraKeys ) { Set < String > notNullExtraKeys = new TreeSet <> ( ) ; for ( String extraKey : extraKeys ) { if ( ! actual . get ( extraKey ) . isNull ( ) ) { notNullExtraKeys . add ( extraKey ) ; } } return notNullExtraKeys ; }
Returns extra keys that are not null .