How else stament made this changes?

Hi guys, I am in week 9 (Exercise 24) from the MOOC  course and I want to know how the else statement change the output... For instance:

public void add(String word, String entry) {

        if(!this.dictionary.containsKey(word)){
            this.dictionary.put(word, new HashSet<String>());
        }
        else{

            this.dictionary.get(word).add(entry);
        }
    }



Output:
[spruce]
null

Version 2: (not "else")
[six, spruce]
null