question: public static String [ ] unionArrays ( String [ ] array1 , String [ ] array2 ) { if ( array1 == null ) { return array2 ; } if ( array2 == null ) { return array1 ; } Set < String > set = new LinkedHashSet < > ( ) ; set . addAll ( Arrays . asList ( array1 ) ) ; set . addAll ( Arrays . asList ( array2 ) ) ; return set . toArray ( new String [ set . size ( ) ] ) ; }
target:  Returns a union of 2 arrays, ensuring that each string exists only once.