rename ErrorCancellable -> EmptyCancellable for flexibility

Author: designatednerd

Sources/Apollo/Cancellable.swift

@@ -12,8 +12,8 @@ extension URLSessionTask: Cancellable {}
 
 // MARK: - Early-Exit Helper
 
-/// A class to return when an error that should cause us to bail out of something still needs to return `Cancellable`.
-public final class ErrorCancellable: Cancellable {
+/// A class to return when we need to bail out of something which still needs to return `Cancellable`.
+public final class EmptyCancellable: Cancellable {
 
   // Needs to be public so this can be instantiated outside of the current framework.
   public init() {}

Sources/ApolloWebSocket/WebSocketTransport.swift

@@ -64,7 +64,7 @@ public class WebSocketTransport: NetworkTransport, WebSocketDelegate {
   public func send<Operation>(operation: Operation, completionHandler: @escaping (_ response: GraphQLResponse<Operation>?, _ error: Error?) -> Void) -> Cancellable {
     if let error = self.error {
         completionHandler(nil,error)
-        return ErrorCancellable()
+        return EmptyCancellable()
     }
 
     return WebSocketTask(self,operation) { (body, error) in