Am a beginner learner. Need help on Trie implementation for longest common prefix.

Single character and single word test cases are failing
For example: {“a”}

Have written the following code which works fine locally with the failed test case on LeetCode
Please tell if you find any logical errors

“
class Solution {

static class Node {
    Node[] children;
    int childCount;
    boolean eow;

    Node(){
        children = new Node[26];
        for (int i = 0; i < 26; i++){
            children[i] = null;
        }
        eow = false;
    }
}

static void insertNode(String str){
    Node current = root;
    for (int i = 0; i < str.length(); i++){
        int index = str.charAt(i)-'a';
        if (current.children[index] == null){
            current.children[index] = new Node();
            current.childCount++;
        }
        if (i == str.length()-1){
            current.children[index].eow = true;
        }
        current = current.children[index];
    }
}


static String longestCommonPrefix() {
    Node current = root;
    String prefix = "";
    if (current.childCount == 0)
        return "";
    while (current.childCount == 1) {
        for (int i =0; i < 26; i++) {
            if (current.children[i] != null){
                prefix += (char)(i+'a');
                current = current.children[i];
                break;
            }
        }

    }

    return prefix;
}

static Node root = new Node();
public static void main(String[] strs) {
    strs = new String[]{"a"};
    for (String s : strs) {
        insertNode(s);
    }
    System.out.println(longestCommonPrefix());
}

}
“

Tried to implement Trie to solve Longest Common Prefix Problem on LeetCode but am failing single character input case -> {“a”}
Works fine locally.