Issue with JSON fields in Laravel

Output

Shift {#278 ▼
  #fillable: array:10 [▶]
  #connection: null
  #table: null
  #primaryKey: "id"
  #perPage: 15
  +incrementing: true
  +timestamps: true
  #attributes: array:12 [▼
    "department_id" => "26"
    "shift_data_id" => "56"
    "dates" => "["2017-06-06","2017-06-08","2017-06-10","2017-06-12"]"
    "start_time" => "0:00"
    "end_time" => "24:00"
    "duration" => "12:00"
    "volunteers" => "4"
    "start_date" => "2017-06-06"
    "end_date" => "2017-06-12"
    "updated_at" => "2017-02-06 07:34:14"
    "created_at" => "2017-02-06 07:34:14"
    "id" => 131
  ]
  #original: array:12 [▶]
  #relations: []
  #hidden: []
  #visible: []
  #appends: []
  #guarded: array:1 [▶]
  #dates: []
  #dateFormat: null
  #casts: []
  #touches: []
  #observables: []
  #with: []
  #morphClass: null
  +exists: true
  +wasRecentlyCreated: true
  #forceDeleting: false
}

"["2017-06-06","2017-06-08","2017-06-10","2017-06-12"]"

Shift {#278 ▼
  #fillable: array:10 [▶]
  #connection: null
  #table: null
  #primaryKey: "id"
  #perPage: 15
  +incrementing: true
  +timestamps: true
  #attributes: array:12 [▼
    "department_id" => "26"
    "shift_data_id" => "56"
    "dates" => "["2017-06-06","2017-06-08","2017-06-10","2017-06-12"]"
    "start_time" => "0:00"
    "end_time" => "24:00"
    "duration" => "12:00"
    "volunteers" => "4"
    "start_date" => "2017-06-06"
    "end_date" => "2017-06-12"
    "updated_at" => "2017-02-06 07:34:14"
    "created_at" => "2017-02-06 07:34:14"
    "id" => 131
  ]
  #original: array:12 [▶]
  #relations: []
  #hidden: []
  #visible: []
  #appends: []
  #guarded: array:1 [▶]
  #dates: []
  #dateFormat: null
  #casts: []
  #touches: []
  #observables: []
  #with: []
  #morphClass: null
  +exists: true
  +wasRecentlyCreated: true
  #forceDeleting: false
}

[]

ScheduleController.php

<?php
    // Create a new schedule
    public function create(ScheduleRequest $request)
    {
        $this->authorize('create-schedule');
        $input = $request->all();

        //...
        
        $input['dates'] = json_encode($input['dates']);

        //...
        
        $schedule = Shift::create($input);

dump($schedule);
dump($schedule->dates);

        // Generate slots based on schedule options
        Slot::generate($schedule);
        
        //...
    }

Slot.php

<?php

    static public function generate(Shift $shift)
    {

        //...


dump($shift);
dd($shift->dates);

        //...
    }