Magento – REST Api Products response not showing extension attributes

I am making following REST API call to get product list, response for this API has extension_attributes tag, but in response these tags are missing.

V1/products?searchCriteria[filter_groups][0][filters][0][field]='.$field.'&searchCriteria[filter_groups][0][filters][0][value]='. $value.'&searchCriteria[filter_groups][0][filters][0][condition_type]='.$condition_type;

Response

{"items":[{"id":1,"sku":"24-MB01","name":"Joust Duffle Bag","attribute_set_id":15,"price":34,"status":1,"visibility":4,"type_id":"simple","created_at":"2016-06-26 16:01:55","updated_at":"2016-07-02 06:45:32","product_links":[{"sku":"24-MB01","link_type":"upsell","linked_product_sku":"24-MB03","linked_product_type":"simple","position":null,"extension_attributes":[]},{"sku":"24-MB01","link_type":"upsell","linked_product_sku":"24-MB05","linked_product_type":"simple","position":null,"extension_attributes":[]},{"sku":"24-MB01","link_type":"upsell","linked_product_sku":"24-MB06","linked_product_type":"simple","position":null,"extension_attributes":[]},{"sku":"24-MB01","link_type":"upsell","linked_product_sku":"24-MB02","linked_product_type":"simple","position":null,"extension_attributes":[]},{"sku":"24-MB01","link_type":"upsell","linked_product_sku":"24-UB02","linked_product_type":"simple","position":null,"extension_attributes":[]},{"sku":"24-MB01","link_type":"upsell","linked_product_sku":"24-WB03","linked_product_type":"simple","position":null,"extension_attributes":[]},{"sku":"24-MB01","link_type":"upsell","linked_product_sku":"24-WB07","linked_product_type":"simple","position":null,"extension_attributes":[]},{"sku":"24-MB01","link_type":"upsell","linked_product_sku":"24-WB04","linked_product_type":"simple","position":null,"extension_attributes":[]}],"options":[],"tier_prices":[],"custom_attributes":[{"attribute_code":"description","value":"<p>The sporty Joust Duffle Bag can't be beat - not in the gym, not on the luggage carousel, not anywhere. Big enough to haul a basketball or soccer ball and some sneakers with plenty of room to spare, it's ideal for athletes with places to go.<p>\r\n<ul>\r\n<li>Dual top handles.<\/li>\r\n<li>Adjustable shoulder strap.<\/li>\r\n<li>Full-length zipper.<\/li>\r\n<li>L 29\" x W 13\" x H 11\".<\/li>\r\n<\/ul>"},{"attribute_code":"image","value":"\/m\/b\/mb01-blue-0.jpg"},{"attribute_code":"small_image","value":"\/m\/b\/mb01-blue-0.jpg"},{"attribute_code":"thumbnail","value":"\/m\/b\/mb01-blue-0.jpg"},{"attribute_code":"options_container","value":"container2"},{"attribute_code":"required_options","value":"0"},{"attribute_code":"has_options","value":"0"},{"attribute_code":"image_label","value":"Image"},{"attribute_code":"small_image_label","value":"Image"},{"attribute_code":"thumbnail_label","value":"Image"},{"attribute_code":"msrp_display_actual_price_type","value":"0"},{"attribute_code":"url_key","value":"joust-duffle-bag"},{"attribute_code":"tax_class_id","value":"2"},{"attribute_code":"activity","value":"11,19,21,22"},{"attribute_code":"style_bags","value":"25,26,29"},{"attribute_code":"material","value":"37,38"},{"attribute_code":"strap_bags","value":"61,62,63,64,65,66"},{"attribute_code":"features_bags","value":"74,76,79"},{"attribute_code":"eco_collection","value":"0"},{"attribute_code":"performance_fabric","value":"0"},{"attribute_code":"erin_recommends","value":"0"},{"attribute_code":"new","value":"0"},{"attribute_code":"sale","value":"0"}]}],"search_criteria":{"filter_groups":[{"filters":[{"field":"sku","value":"24-MB01","condition_type":"eq"}]}]},"total_count":1}

How can I get extension_attributes in the response? Extension_attributes are available in Product search based on sku.