检查数组是否为空，是否从具有CSRF生成令牌的FORM接收到该数组

Since I am using csrf in the form, the array $data that is passed in request function is never empty. How to resolve this so that when i submit the form without any input fields filled, I get "data is empty"?

view.blade.php

<form action="{{url('/userdata')}}" method="POST">
    @csrf
    <div class="form-group">
        <label for="name">Name:</label>
        <input type="text" class="form-control" name="name">
    </div>
    <button type="submit" class="btn btn-default">Submit</button>
</form>

Controller.php

public function userdata(Request $request)
{
    $data=$request ->all();
    if(!empty($data)){
        echo "data is filled";
    }else{
        echo "data is empty";
    }
}

Sorry I misunderstood your question on my first answer. A value will always be submitted for input elements on the page, even if they're empty. The proper way to do this is to create a request validation.

Create something like this class, though much neater I'm sure ;)

<?php
namespace App\Http\Requests;
use Illuminate\Foundation\Http\FormRequest;
class StoreUserdata extends FormRequest {
    public function authorize() {return true;}
    public function rules() {
        return ["name" => ["required", "max:64"]];
    }
}

And then edit the signature of your controller method so instead of expecting a Request it looks for your validation class (don't forget a use statement above):

public function userdata(StoreUserdata $request){
// ....
}

Now, your requests will fail if the name input is empty, or is too long. There are a lot of possible validation rules.

You can use required in the input fields if you don't want the form to submit empty.

<form action="{{url('/userdata')}}" method="POST">
    @csrf
    <div class="form-group">
        <label for="name">Name:</label>
        <input type="text" class="form-control" name="name" required>
    </div>
    <button type="submit" class="btn btn-default">Submit</button>
</form>

Otherwise if name is your only field you can do this:

public function userdata(Request $request){
    $data = $request->except(["_token"]);
    if($data['name'] != ""){
      echo "data is filled";
    } else {
      echo "data is empty";
    }
}

You can use the get() method:

public function userdata(Request $request){
    $data = $request->get("_token");
    if(!empty($data)){
      echo "data is filled";
    } else {
      echo "data is empty";
    }
}