Hi,
The error is based on "$element->characteristics" not on the variants, my apologize.
Can you try to replace the code:
				foreach($element->characteristics as $k2 => $characteristic2){
					if(!empty($variant->characteristics)){
						foreach($variant->characteristics as $k3 => $characteristic3){
							if($k2==$k3){
								$temp[$k3]=$characteristic3;
								break;
							}
						}
					}
				}To:
                          if(is_array($element->characteristics){
				foreach($element->characteristics as $k2 => $characteristic2){
					if(!empty($variant->characteristics)){
						foreach($variant->characteristics as $k3 => $characteristic3){
							if($k2==$k3){
								$temp[$k3]=$characteristic3;
								break;
							}
						}
					}
				}
                        }