product.metafields.custom["size"] =>
product.metafields.custom.size => 3

product.metafields.custom["first"] =>
product.metafields.custom.first => booleanfalse

product.metafields.custom["last"] =>
product.metafields.custom.last =>

product.metafields.custom["to_h"] => value of metafield to_h
product.metafields.custom.to_h => value of metafield to_h

product.metafields.custom["to_liquid"] =>
product.metafields.custom.to_liquid =>