Null pointer Exception

Question

screen shot of the errorI have written the following code to solve the Longest SubStrings With All Unique Characters. How can I fix this issue? , I understand what a null pointer exception is and why am I getting it , the question is what changes could be done such that I get the result based on the question. Again , what could be changed logically in this particular piece of code to make it work as its intended ,

receiving a null pointer exception

public class LongestSubStringWithAllUniqueChars {


static Map findUnique(char[] arr , int l , int r){
    Map<Character,Integer> map = new HashMap();
    for(int i=l;i<r;i++){
        if(map.containsKey(arr[l])){
            map.put(arr[l],map.get(arr[l])+1);
        }else{
            map.put(arr[l],1);
        }
    }
    map.forEach((c,v) ->{
        System.out.println(c+" "+v);
    });
    return map;
}
public static void main(String[] args) {
    String str = "GEEKSFORGEEKS";
    char[] arr = str.toCharArray();
    int l = 0;int r=0;
    int max =0;
    Map map  = new HashMap<>();


    while(r<arr.length){
        r++;
        map = findUnique(arr,l,r);
        if(map.size() < r-l+1){
            r++;
            map.put(arr[l],(int)map.get(arr[l])-1);
            while(map.size()< r-l+1){
                map.remove(arr[l],(int)map.get(arr[l])); // getting nullpointer here
                l++;
            }

        } else if(map.size()==r-l+1){
            max = r-l+1;
            r++;
        }
    }
    System.out.println(max);

}

}