cannot use 'in' operator to search for 'length' in ajax Laravel

I want to display message with ajax  :
but i have this error in the console :
Cannot use 'in' operator to search for 'length' in L'email ou le mot de passe est incorrect.

Function Ajax

<script type="text/javascript">
   $(document).ready(function() {
        $(".login-btn").click(function(e){
             e.preventDefault();


            var _token = $("input[name='_token']").val();
            var email = $("input[name='email']").val();
            var password = $("input[name='password']").val();


            $.ajax({
                url: "/login",
                type:'POST',
                cache: false,
                data: {_token:_token,email:email, password:password},
                dataType: "json",
                success: function(data) {
                    if($.isEmptyObject(data.error)){
                        window.location = 'home';
                    }else{
                        // $(".print-error-msg").find("ul").html('');
                        // $(".print-error-msg").css('display','block');
                        // $.each( data, function( key, value ) {
                        //     $(".print-error-msg").find("ul").append('<li>'+data.error+'</li>+');
                        // });
                        printErrorMsg (data.error);

                    }
                },
                error: function(response){
                    $(".print-error-msg").find("ul").html('');
                    $(".print-error-msg").css('display','block');
                    $(".print-error-msg").find("ul").append('<li>'+response.responseJSON.error+'</li>');
                    
                }
            });


        });  
         function printErrorMsg (msg) {
            $(".print-error-msg").find("ul").html('');
            $(".print-error-msg").css('display','block');
            $.each( msg, function( key, value ) {
                $(".print-error-msg").find("ul").append('<li>'+value+'</li>');
            });
        }
    });
</script>

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Code de function laravel in the controller

  public function loginPost(Request $request){
 
        $rules = array(
            'email' => 'required|email|exists:users',
            'password' => 'required');
            
 
            $validator = Validator::make(Input::all() , $rules);
 
            if ($validator->fails())
                {
                 return response()->json(['error'=>$validator->errors()->all()]);

                }
              else
                {
                $userdata = array(
                    'email' => Input::get('email') ,
                    'password' => Input::get('password')
                );
 
                if (Auth::attempt(['email' => Request::get('email'), 'password' => Request::get('password')]))
                {
                    return redirect()->intended();
                }
                else
                {
                   return response()->json(['error'=>'L\'email ou le mot de passe est incorrect.'], 200);
                }
                }

            }

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the view code:

@extends('layouts.app')

@section('content')
<div class="container">
    <div class="row">
        <div class="col-md-8 col-md-offset-2">
            <div class="panel panel-default">
                <div class="panel-heading">Login</div>
                <div class="panel-body">
                    <!-- <div class="alert-danger" style="display:none">
                    </div> -->
                    <div class="alert alert-danger print-error-msg" style="display:none">
                        <ul>
                            <li></li>
                        </ul>
                    </div>
                    <form class="form-horizontal" role="form" id="btn-login" method="POST" action="{{ url('/login') }}">
                        {{ csrf_field() }}

                        <div class="form-group{{ $errors->has('email') ? ' has-error' : '' }}">
                            <label for="email" class="col-md-4 control-label">E-Mail Address</label>

                            <div class="col-md-6">
                                <input id="email" type="email" class="form-control" name="email" value="{{ old('email') }}">

                                @if ($errors->has('email'))
                                    <span class="help-block">
                                        <strong>{{ $errors->first('email') }}</strong>
                                    </span>
                                @endif
                            </div>
                        </div>

                        <div class="form-group{{ $errors->has('password') ? ' has-error' : '' }}">
                            <label for="password" class="col-md-4 control-label">Password</label>

                            <div class="col-md-6">
                                <input id="password" type="password" class="form-control" name="password">

                                @if ($errors->has('password'))
                                    <span class="help-block">
                                        <strong>{{ $errors->first('password') }}</strong>
                                    </span>
                                @endif
                            </div>
                        </div>

                        <div class="form-group">
                            <div class="col-md-6 col-md-offset-4">
                                <div class="checkbox">
                                    <label>
                                        <input type="checkbox" name="remember"> Remember Me
                                    </label>
                                </div>
                            </div>
                        </div>

                        <div class="form-group">
                            <div class="col-md-6 col-md-offset-4">
                                <button type="submit" class="btn btn-primary login-btn">
                                    <i class="fa fa-btn fa-sign-in"></i> Login
                                </button>

                                <a class="btn btn-link" href="{{ url('/password/reset') }}">Forgot Your Password?</a>
                            </div>
                        </div>
                    </form>
                </div>
            </div>
        </div>
    </div>
</div>
@endsection

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