TypeError: Cannot convert undefined or null to object

[Figzyy]

I've ran into this issue. As soon as a socket is connected the server shuts down because of this error.
Not sure how this is happening.

1 function getAllPlayers(){
2    var players = [];
3    
4    Object.keys(io.sockets.connected).forEach(function(socketID){
5        var player = io.sockets.connected[socketID].player;
6        if(player) players.push(player);
7    });
8    return players;
}

Line 4 seems to be the issue.

TypeError: Cannot convert undefined or null to object
at Function.keys ()