fixup! util/vizerror: add new package for visible errors

Signed-off-by: Will Norris <will@tailscale.com>

util/vizerror/vizerror.go

@@ -20,13 +20,13 @@ func (e Error) Error() string {
 	return e.err.Error()
 }
 
-// New returns an Error that formats as the given text.
-func New(text string) Error {
+// New returns an error that formats as the given text. Always returns a vizerror.Error.
+func New(text string) error {
 	return Error{errors.New(text)}
 }
 
-// Errorf returns an Error with the specified format and values.
-func Errorf(format string, a ...any) Error {
+// Errorf returns an Error with the specified format and values. Always returns a vizerror.Error.
+func Errorf(format string, a ...any) error {
 	return Error{fmt.Errorf(format, a...)}
 }
 
@@ -36,6 +36,9 @@ func (e Error) Unwrap() error {
 }
 
 // Wrap err with a vizerror.Error.
-func Wrap(err error) Error {
+func Wrap(err error) error {
+	if err == nil {
+		return nil
+	}
 	return Error{err}
 }