dagger/dagger · error

nil change

Error message

nil change

What it means

Defensive nil guard at the top of applier.Apply: the caller passed a nil *change to the diff applier. Changes are produced internally by the diff/apply machinery, so this indicates an upstream bookkeeping bug or an uninitialized change in user-authored extensions of that pipeline.

Source

Thrown at engine/snapshots/diffapply_linux.go:201

		}
		a.root = root
		prevRelease := a.release
		a.release = func() error {
			err := mnter.Unmount()
			return multierror.Append(err, prevRelease()).ErrorOrNil()
		}
	}

	a.root, err = filepath.EvalSymlinks(a.root)
	if err != nil {
		return nil, errors.Wrapf(err, "failed to resolve symlinks in %s", a.root)
	}
	return a, nil
}

func (a *applier) Apply(ctx context.Context, c *change) error {
	if c == nil {
		return errors.New("nil change")
	}

	if c.kind == continuityfs.ChangeKindUnmodified {
		return nil
	}

	dstPath, err := safeJoin(a.root, c.subPath)
	if err != nil {
		return errors.Wrapf(err, "failed to join paths %q and %q", a.root, c.subPath)
	}
	var dstStat *syscall.Stat_t
	if dstfi, err := os.Lstat(dstPath); err == nil {
		stat, ok := dstfi.Sys().(*syscall.Stat_t)
		if !ok {
			return errors.Errorf("failed to get stat_t for %T", dstStat)
		}
		dstStat = stat
	} else if !os.IsNotExist(err) {

View on GitHub (pinned to 82ba2681db)

Solutions

1. Check for nil before calling Apply and skip or log the entry
2. Fix the walker/callback so it never emits nil changes
3. Ensure error paths that would produce a nil change return the error instead

Example fix

// before
applier.Apply(ctx, c) // c may be nil
// after
if c == nil { return nil } // or log & skip
applier.Apply(ctx, c)

if c == nil {
  return errors.New("cannot apply nil change")
}
_ = applier.Apply(ctx, c)

func validChange(c *change) bool { return c != nil }

When it happens

Trigger: Passing nil directly to (*applier).Apply, or a change-walk callback that appends nil entries into the change channel/slice.

Common situations: Custom continuityfs walkers that yield nil on skipped entries; bugs in code that builds the change list (e.g. returning nil from a factory on error without checking).

Related errors

• failed to get global configuration: %w
• collect ID requires handle-form ID
• workspace is required
• bind session resource: nil cache
• bind session resource: empty session ID

AI-assisted analysis of dagger/dagger@82ba2681db (2026-09-05). Data as JSON: /api/errors/4a1ff0c8f93b98f2. Report an issue: GitHub.