ManagedUpload.send's callback may return null instead of an Error (#3904

)

Co-authored-by: Christian Paul <christianp@element.io>

lib/s3/managed_upload.d.ts

@@ -16,7 +16,7 @@ export class ManagedUpload {
     /**
      * Initiates the managed upload for the payload.
      */
-    send(callback?: (err: AWSError, data: ManagedUpload.SendData) => void): void;
+    send(callback?: (err: AWSError|null, data: ManagedUpload.SendData) => void): void;
     /**
      * Adds a listener that is triggered when theuploader has uploaded more data.
      *