First Non-Repeating Character

import java.util.*;
class Main {
    public static void main(String[] args) {
        System.out.println(new Main().nonRepeatingCharacter("hello"));
        System.out.println(new Main().nonRepeatingCharacter("abbazz"));
         System.out.println(new Main().nonRepeatingCharacter("abbqqad"));
         System.out.println(new Main().nonRepeatingCharacter(""));
    }
    
    public String nonRepeatingCharacter(String s){
        if(s.isEmpty()){
            return "None";
        }
        
        Map<Character, Integer> charMap = new HashMap<>();
        
        for(int i = 0 ; i< s.length(); i++){
            char ch = s.charAt(i);
            if(charMap.get(ch)==null){
                charMap.put(ch,1);
            }
            else{
                Integer value = charMap.get(ch);
                charMap.put(ch,++value);
            }
            
        }
        
        for(int i =0 ; i<s.length(); i++){
            if(charMap.get(s.charAt(i))==1){
                return String.valueOf(s.charAt(i));
            }
        }
        return "None";
        
    }
}

// I can ask, lower and upper case
// edge cases like empty string