Laravel : $request->hasFile() is not working Call to a member function getClientOriginalExtension() on string

I am working with laravel 5.6 for upload a file using HTML form but I am having a problem while retrieving a file in a controller.

When I retrieve it using this way it returns ok return $request; it is retrieving in controller but not in hasFile() function or getClientOriginalExtension()

I have searched many website but problem is still staying here. All I have matched but not working.

Error: "Call to a member function getClientOriginalExtension() on null"

Html Form view:

<form  action="" enctype="multipart/form-data" method="post">
    
    <input type="file" name="photo" id="photo"  class="btn btn-secondary">
    <hr>
    <button type="submit" value="upload" class="form-control btn btn-primary btn-fill btn-lg">Upload Image</button>
</form>

Route:

Route::post('/changeProductImage','ProductsController@upload');

Controller:

function upload(Request $request)
{
     $image = $request->file('photo');

     $new_name = rand() . '.' . $image->getClientOriginalExtension();

     $image->move(public_path('images'), $new_name);
     return back()->with('success', 'Image Uploaded Successfully');
}

via Chebli Mohamed