Null value as key in Java HashMap

import java.util.HashMap;
import java.util.Map;
public class Demo {
	public static final void main(String[] args) {
		Map<String,String>map = new HashMap<>();
		map.put("Football", "A");
		map.put("Squash", "B");
		map.put("Cricket", "C");
		map.put("Hockey", "D");
		map.put("Rugby", "E");
		map.put("Golf", "F");
		map.put("Archery", "G");
		System.out.println("Size of HashMap = " + map.size());
		map.put(null, "H");
		System.out.println("Updated Size of HashMap = " + map.size());
		System.out.println("For null = " + map.get(null));
	}
}