Why doesn't AppCtrl have $inject but MyCtrl1 does in this AngularJS example?

I am looking at this angularjs/socket.io example, but I was wondering why AppCtrl doesn't have a $inject line and MyCtrl1 does?

controllers.js:

'use strict';

/* Controllers */

function AppCtrl($scope, socket) {
  socket.on('send:name', function (data) {
    $scope.name = data.name;
  });
}

function MyCtrl1($scope, socket) {
  socket.on('send:time', function (data) {
    $scope.time = data.time;
  });
}
MyCtrl1.$inject = ['$scope', 'socket'];


function MyCtrl2() {
}
MyCtrl2.$inject = [];

See: https://github.com/btford/angular-socket-io-seed/blob/master/public/js/controllers.js