JAVA

Why the else statement changes the output?

I want to know how the else statement change the output in this way if it is supposed to do the same thing as the second output... so Why?

if we add an else statement the outputs is:

[spruce]

null

and without is:

[six, spruce]

null

this is the code that causes this issue:

public void add(String word, String entry) { if(!this.dictionary.containsKey(word)){ this.dictionary.put(word, new HashSet()); } this.dictionary.get(word).add(entry); }