to_s:
size: 18
to_json:
first: 1_testgid://shopify/Metaobject/77187153942
product.metafields.custom["size"] =>
product.metafields.custom.size => 18

product.metafields.custom["first"] =>
product.metafields.custom.first => 1_testgid://shopify/Metaobject/77187153942

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

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

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