FileInputStream wirft NullPointerException

Erhalte ich die nullpointerexception, weiß nicht, was es eigentlich ist, was es ist. Ich lese aus den java-docs, die fileinputstream nur throws securityexception also nicht verstehen, warum diese Ausnahme erscheint.
hier ist mein code-snippet.

private Properties prop = new Properties();
private String settings_file_name = "settings.properties";
private String settings_dir = "\\.autograder\\";

public Properties get_settings() {
    String path = this.get_settings_directory();
    System.out.println(path + this.settings_dir + this.settings_file_name);
    if (this.settings_exist(path)) {
        try {
            FileInputStream in = new FileInputStream(path + this.settings_dir + this.settings_file_name);
            this.prop.load(in);
            in.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    } else {
        this.create_settings_file(path);
        try{
            this.prop.load(new FileInputStream(path + this.settings_dir + this.settings_file_name));
        }catch (IOException ex){
            //ex.printStackTrace();
        }
    }
    return this.prop;
}

private String get_settings_directory() {
    String user_home = System.getProperty("user.home");
    if (user_home == null) {
        throw new IllegalStateException("user.home==null");
    }

    return user_home;
}

und hier ist mein stacktrace:

C:\Users\mohamed\.autograder\settings.properties
Exception in thread "main" java.lang.NullPointerException
        at autograder.Settings.get_settings(Settings.java:41)
        at autograder.Application.start(Application.java:20)
        at autograder.Main.main(Main.java:19)
Java Result: 1
BUILD SUCCESSFUL (total time: 0 seconds)

Line 41 is: this.prop.load(in);