Error with custom list

[TechPro424]

Added

@Gui.CollapsibleObject
    public ArrayList<Group> groups = new ArrayList<Group>();

to my config class, and I get this error: https://gist.github.com/TechPro424/196d9e0542eed2ba557d32141143ab9e

Here is the Group class that I am using in the ArrayList

package in.techpro424.groupmessages.config;

import java.util.ArrayList;

public class Group {
    String name =  "group1";
    public ArrayList<String> playerNames = new ArrayList<String>();

    public Group(String name, ArrayList<String> arrayList) {
        this.name = name;
        this.playerNames = arrayList;
    }
}

Please help me out