Laravel Eloquent belongsto relationship returns null

Title: Understanding Laravel Eloquent BelongsTo Relationship and Null Return Issue Body:

In the world of software development, Laravel is an incredibly popular PHP framework that makes web application development more efficient. One of its key components, Eloquent, offers Object-Relational Mapping (ORM) capabilities that enable you to interact with your database in a user-friendly manner. However, you might run into issues when working with relationships and NULL return values.

To set up the example that we will discuss, let's look at two Eloquent models:

1) Post:

class Post extends Model
{
    protected $table = 'posts';
    protected $fillable = ['id', 'user_id', 'product_id', 'site_id', 'link_id', 'body', 'created_at', 'updated_at'];

    public function user(){
        return $this->belongsTo(User::class);
    }

    public function product(){
        return $this->belongsTo(Product::class);
    }
}

2) Product:

protected $table = 'products';
protected $fillable = ['id', 'user_id', 'manufacturer_id', 'shift_product_id', 'name', 'english_name',
                        'slug', 'text', 'spec', 'live', 'created_at', 'updated_at'];

public function posts(){
    return $this->hasMany(Post::class);
}

Your goal is to get the related product from a post. Let's first see what happens when you perform the following:

$posts = Post::get();

foreach($posts as $key){
    dd($key->product);
}

The result is that all posts return NULL instead of the related product. This can cause problems when trying to use this information in your app. This issue mainly occurs due to missing data or incorrect data from the database. To diagnose the problem, you should check your Post and Product tables for any missing foreign keys or mismatched relationships. If your tables are properly set up, another possible reason for the NULL return could be that a relationship doesn't exist between the post and its related product. In this case, make sure to verify whether a product is indeed linked to each post you're querying. If no connection exists, Laravel will naturally return NULL since there's nothing to relate to. The solution might depend on your application's specific requirements. For instance, if your app requires all posts to have their related products and the absence of a product-post relationship shouldn't happen, you could handle this error by throwing an exception or setting up custom validation rules for your models. On the other hand, if you want to manage missing relationships gracefully, consider using optional chaining.

To use optional chaining, modify your code as follows:

$posts = Post::get();

foreach($posts as $key){
    dd($key->product?->name); // Optional chaining checks for the product and uses its 'name' attribute if available.
}

In conclusion, understanding Laravel Eloquent belongsTo relationships and their associated null return values is essential for building efficient web applications. By diagnosing database issues and adapting your code accordingly, you can ensure a smooth user experience and avoid potential problems in your application's functionality.