api/checkpoint: Don't return null if no checkpoints

vvoland · vvoland · commit 646e068cf165 · 2025-09-26T16:45:04.000+02:00
This fixes a bug where no checkpoints would produce a `null` response
instead of an empty array:

```
$ docker run -d --name foo nginx:alpine
17fbeff7185733f101c38cb8208359dd0ef141116a1345da2d3c3f58c11f3e14

$ curl --unix-socket /var/run/docker.sock http://local/containers/foo/checkpoints
null
```

With this patch, this becomes:
```
$ curl --unix-socket /var/run/docker.sock http://local/containers/foo/checkpoints
[]
```

Signed-off-by: Paweł Gronowski &lt;pawel.gronowski@docker.com&gt;
diff --git a/daemon/server/router/checkpoint/checkpoint_routes.go b/daemon/server/router/checkpoint/checkpoint_routes.go
@@ -39,6 +39,9 @@ func (cr *checkpointRouter) getContainerCheckpoints(ctx context.Context, w http.
 	if err != nil {
 		return err
 	}
+	if checkpoints == nil {
+		checkpoints = []checkpoint.Summary{}
+	}
 
 	return httputils.WriteJSON(w, http.StatusOK, checkpoints)
 }

Original file line number	Diff line number	Diff line change
`@@ -39,6 +39,9 @@ func (cr *checkpointRouter) getContainerCheckpoints(ctx context.Context, w http.`
`39`	`39`	`if err != nil {`
`40`	`40`	`return err`
`41`	`41`	`}`
	`42`	`+ if checkpoints == nil {`
	`43`	`+ checkpoints = []checkpoint.Summary{}`
	`44`	`+ }`
`42`	`45`
`43`	`46`	`return httputils.WriteJSON(w, http.StatusOK, checkpoints)`
`44`	`47`	`}`