state that the server may send a subset of fields by default

- the subset may be empty
- fields[type]= can be used to request no fields
- see json-api#1499

Author: freddrake

_format/1.0/index.md

@@ -1000,11 +1000,16 @@ response on a per-type basis by including a `fields[TYPE]` parameter.
 
 The value of the `fields` parameter **MUST** be a comma-separated (U+002C
 COMMA, ",") list that refers to the name(s) of the fields to be returned.
+An empty value indicates that no fields should be returned.
 
 If a client requests a restricted set of [fields] for a given resource type,
 an endpoint **MUST NOT** include additional [fields] in resource objects of
 that type in its response.
 
+If a client does not specify the set of [fields] for a given resource type,
+the server **MAY** send a subset of the set of fields defined for the resource
+type; an empty set is acceptable.
+
 ```http
 GET /articles?include=author&fields[articles]=title,body&fields[people]=name HTTP/1.1
 Accept: application/vnd.api+json

_format/1.1/index.md

@@ -1151,11 +1151,16 @@ response on a per-type basis by including a `fields[TYPE]` query parameter.
 
 The value of any `fields[TYPE]` parameter **MUST** be a comma-separated (U+002C
 COMMA, ",") list that refers to the name(s) of the fields to be returned.
+An empty value indicates that no fields should be returned.
 
 If a client requests a restricted set of [fields] for a given resource type,
 an endpoint **MUST NOT** include additional [fields] in resource objects of
 that type in its response.
 
+If a client does not specify the set of [fields] for a given resource type,
+the server **MAY** send a subset of the set of fields defined for the resource
+type; an empty set is acceptable.
+
 ```http
 GET /articles?include=author&fields[articles]=title,body&fields[people]=name HTTP/1.1
 Accept: application/vnd.api+json