User Login with SQLite database java.lang.NullPointerException

I'm having a problem using my database to check the username and password of the user. I'm using a query to select the specific row and then check the password against what was entered by the user. The error I am getting is a java.lang.NullPointerException in my login page when i call the

Users userlogin = db.userlogin(usernameinput);

After looking at the method I'm thinking its the first cursor that causes it to fail

cursor.getInt(0);

What I'm wondering is am I right in thinking this and what can I do to change it? I've tried changing the if statement to

If(cursor.getcount() > 0)

and still no luck.

public class LoginPage extends ActionBarActivity {
        Button loginbutton;
        EditText usernameuser, passworduser;
        DatabaseHandler db;
        String usernameinput, passwordinput;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_login_page);




        loginbutton = (Button) findViewById(R.id.loginbtn);
        usernameuser = (EditText) findViewById(R.id.usernameInsert);
        passworduser = (EditText) findViewById(R.id.passwordInsert);





        loginbutton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                usernameinput = usernameuser.getText().toString();
                passwordinput = passworduser.getText().toString();
                Users userlogin = db.userLogin(usernameinput);
                if (usernameinput.equals(userlogin.get_username()) && passwordinput.equals(userlogin.get_password())) {
                    startActivity(new Intent(getApplicationContext(), Home_Page.class));
                }
                else {
                    Toast.makeText(getApplicationContext(), "Error", Toast.LENGTH_SHORT).show();
                }
            }

        });

Database handler Query used to check login:

public Users userLogin(String username) {

    SQLiteDatabase db = this.getReadableDatabase();
    String[] projection = {KEY_USER_ID, KEY_USERNAME, KEY_PASSWORD};
    String selection = KEY_USERNAME + " =?";
    String[] selectionargs = {username};
   Cursor cursor = db.query(TABLE_USERS, projection, selection, selectionargs, null, null,null );
    if (cursor != null)
        cursor.moveToFirst();
            Users users = new Users(
                    cursor.getInt(0),
                    cursor.getString(1),
                    cursor.getString(2),
                    cursor.getInt(3),
                    cursor.getString(4),
                    cursor.getString(5),
                    cursor.getDouble(6),
                    cursor.getDouble(7),
                    cursor.getDouble(8),
                    cursor.getDouble(9),
                    cursor.getDouble(10),
                    cursor.getDouble(11),
                    cursor.getDouble(12),
                    cursor.getDouble(13),
                    cursor.getDouble(14),
                    cursor.getDouble(15),
                    cursor.getDouble(16),
                    cursor.getDouble(17),
                    cursor.getDouble(18),
                    cursor.getDouble(19));
    cursor.close();
    return users;

}

enter code here