前缀树的新结点（java数组问题）

class Trie {
private Trie[] children;
private boolean isEnd;

public Trie() {
    children = new Trie[26];
    isEnd = false;
}

public void insert(String word) {
    Trie node = this;
    for (int i = 0; i < word.length(); i++) {
        char ch = word.charAt(i);
        int index = ch - 'a';
        if (node.children[index] == null) {
            node.children[index] = new Trie();
        }
        node = node.children[index];
    }
    node.isEnd = true;
}

public boolean search(String word) {
    Trie node = searchPrefix(word);
    return node != null && node.isEnd;
}

public boolean startsWith(String prefix) {
    return searchPrefix(prefix) != null;
}

private Trie searchPrefix(String prefix) {
    Trie node = this;
    for (int i = 0; i < prefix.length(); i++) {
        char ch = prefix.charAt(i);
        int index = ch - 'a';
        if (node.children[index] == null) {
            return null;
        }
        node = node.children[index];
    }
    return node;
}

}

这第12行代码什么意思呀，可以来个图解吗

12行的代码是给对应的空节点赋值