Error about BufferedWriter class in java12

Jeewantha Lahiru :

when I run this code I get error.Can you Show me the error?

public static void main(String[] args) throws IOException {
        BufferedWriter bw = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));
        String s = "Hello world";
        bw.write(s);
        bw.newLine();
        bw.close();
    }

I see this code in more hackerrank problems and I need to know why we use this... this is the error message,

Exception in thread "main" java.lang.NullPointerException
    at java.base/java.io.FileOutputStream.<init>(FileOutputStream.java:226)
    at java.base/java.io.FileOutputStream.<init>(FileOutputStream.java:124)
    at java.base/java.io.FileWriter.<init>(FileWriter.java:66)
    at com.company.Main.main(Main.java:8)

Trishul Singh Choudhary :

I guess you didn't give new File try this :

    public static void main(String args[]) throws IOException {
        BufferedWriter bw = new BufferedWriter(new FileWriter(new File("C:\\Users\\myName\\Desktop\\data.txt")));
        String s = "Hello world";
        bw.write(s);
        bw.newLine();
        bw.close();
    }
}

This works fine for me and the txt file is generated as desired. Let me know if it helps.