code: protected function setInstance(Attribute $attribute)
      {
          if ($this->has($attribute->getMetaKey())) {
              $this->update($attribute);
          } else {
              $this->items[$attribute->getMetaKey()] = $attribute;
          }
  
          return $this;
      }
docs: Set attribute.
  
  @param \Sofa\Eloquence\Metable\Attribute $attribute