Error: NullPointerAccess: The variable " " can only be null at this location

I am creating a web service that queries my database and returns a list of the object in the database. I get the error: NullPointerAccess: The variable "varname" can only be null at this location. No matter where I put the variable, I get the same warnings. No matter what I put inside the variable, it returns null. Below is the method that it occurs in:

    public List<Contacts> getUsers()
  {     String test = null;
        String username = "root";
        String password = "ticket";
        String tablename = "users";
        String fieldname = "*";
        String query = "SELECT " + fieldname + " FROM " + "android." + tablename + ";";

        Contacts cont = new Contacts();
        List<Contacts> lstc = null;

        /* this chnk of code can appear more or less verbatim */
        /* in your database apps (including JSPs) */
        String url = "jdbc:mysql://"my IP address":3306/android";
        try{
        Class.forName("com.mysql.jdbc.Driver").newInstance();
        Connection con = DriverManager.getConnection(url, username, password);
        Statement stmt = con.createStatement();
        ResultSet rs = stmt.executeQuery(query);


        while (rs.next()){
            if (!(rs.getString("username") == null)){
             cont.setUsername(rs.getString("username"));
            }
            if (!(rs.getString("location") == null)){
             cont.setLocation(rs.getString("location"));
            }
            if (!(rs.getString("updated_at") == null)){
             cont.setUpdated_at(rs.getDate("updated_at"));
            }
            if (!(rs.getSt开发者_如何转开发ring("idUsers") == null)){
             cont.setId(rs.getInt("idUsers"));
            }
        }

        rs.close();
        stmt.close();
        con.close();
        }catch(Exception e){
            test = e.toString();
        }
         lstc.add(cont); //THIS IS THE VARIABLE THAT IS GIVING THE WARNINGS
        test = "blahbadslf";
        return lstc;
        }

The variable that is getting the warnings is my List lstc variable. When I try to add a Object to the List I get the errors. Any help would be much appreciated. Here is the Class just in case:

public class Contacts{
private int id;
private String username;
private String location;
private Date updated_at;

public void setId(int id) {
    this.id = id;
}
public int getId() {
    return id;
}
public void setUsername(String username) {
    this.username = username;
}
public String getUsername() {
    return username;
}
public void setLocation(String location) {
    this.location = location;
}
public String getLocation() {
    return location;
}
public void setUpdated_at(Date updated_at) {
    this.updated_at = updated_at;
}
public Date getUpdated_at() {
    return updated_at;
}

}

Thanks!

You're getting that message because you have:

List<Contacts> lstc = null;

Did you mean:

List<Contacts> lstc = new ArrayList<Contacts>();

BTW:

You have a second bug:

    Contacts cont = new Contacts();  // you only create one of these

Better:

    while (rs.next()){
        Contacts cont = new Contacts();  // move to within the loop so one is created for every row in the result set

There is this:

List<Contacts> lstc = null;

And then no object is ever assigned to lstc. Fail :(

Consider a new ArrayList<Contacts>() somewhere meaninful (such as in the declaration).

You didn't instantiated the list. The list is still null when you want to access it.

So you should use that:

List<Contacts> lstc = new List<Contacts>();