class that has composite key produce error

[aqualaguna]

Q	A
Bug?	yes
New Feature?	yes
Framework	Laravel
Framework version	5.4.y
Package version	6.0.0
PHP version	7.0.1

Actual Behaviour

i get this error actualy in my project

array_key_exists(): The first argument should be either a string or an integer
at Model->getKey()
in Auditable.php (line 250)

i implement it in my class that has composite key as primary

class PurchaseDetail extends Model implements AuditableContract
{
use HasCompositeKey, Auditable;
public $timestamps = false;
protected $primaryKey = ['purchase_id','item_id','unit_id'];
}

Expected Behaviour

auditable_id : multi primary

Possible Solutions

making the class model not composite primary instead using id with auto increment. this solution may cause duplicate in some record.

[quetzyg]

I'm unaware of Eloquent supporting composite keys.

[quetzyg]

Closing due to lack of information.