add note about final payloads

Author: robrichard

spec/Section 7 -- Response.md

@@ -23,24 +23,29 @@ with key `data`. The value of this entry is described in the "Data" section. If
 the operation failed before execution, due to a syntax error, missing
 information, or validation error, this entry must not be present.
 
+When the response of the GraphQL operation is an event stream, the first value
+will be the initial response. All subsequent values may contain `label` and 
+`path` entries. These two entries are used by clients to identify the the 
+`@defer` or `@stream` directive from the GraphQL operation that triggered this
+value to be returned by the event stream. The combination of these two entries
+must be unique across all values returned by the event stream. 
+
 If the response of the GraphQL operation is an event stream, each response map
 must contain an entry with key `hasNext`. The value of this entry is `true` for
 all but the last response in the stream. The value of this entry is `false` for 
 the last response of the stream. This entry is not required for GraphQL 
-operations that return a single response map.
+operations that return a single response map. 
+
+The GraphQL server may determine there are no more values in the event stream 
+after a previous value with `hasNext`: `true` has been emitted. In this case 
+the last value in the event stream should be a map without `data`, `label`, 
+and `path` entries, and a `hasNext` entry with a value of `false`.
 
 The response map may also contain an entry with key `extensions`. This entry,
 if set, must have a map as its value. This entry is reserved for implementors
 to extend the protocol however they see fit, and hence there are no additional
 restrictions on its contents.
 
-When the response of the GraphQL operation is an event stream, the first value
-will be the initial response. All subsequent values must contain `label` and 
-`path` entries. These two entries are used by clients to identify the the 
-`@defer` or `@stream` directive from the GraphQL operation that triggered this
-value to be returned by the event stream. The combination of these two entries
-must be unique across all values returned by the event stream.
-
 To ensure future changes to the protocol do not break existing servers and
 clients, the top level response map must not contain any entries other than the
 three described above.
@@ -250,7 +255,7 @@ When the `path` field is present on an "Error result", it indicates the response
 ## Label
 
 If the response of the GraphQL operation is an event stream, subsequent values
-will contain a string field `label`. This `label` is the same label passed to 
+may contain a string field `label`. This `label` is the same label passed to 
 the `@defer` or `@stream` directive that triggered this value. This allows 
 clients to identify which `@defer` or `@stream` directive is associated with
 this value.