import java.util.*;

class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		String a = "a";
		String b = null;
		String c = "b";
		
		System.out.println(get(a) + get(b));
		System.out.println(get(a) + get(b) + get(c));
		System.out.println(get(b));
	}
	
	public static String get(String string){
		return Optional.ofNullable(string).orElse("");
	}
}