Additional generator tests.

internal/utils/errfmt/errfmt.go

@@ -1,10 +1,14 @@
 package errfmt
 
 import (
+	"github.com/go-jet/jet/v2/internal/utils/is"
 	"strings"
 )
 
 // Trace returns well formatted wrapped error trace string
 func Trace(err error) string {
+	if is.Nil(err) {
+		return ""
+	}
 	return "Error trace:\n" + " - " + strings.Replace(err.Error(), ": ", ":\n - ", -1)
 }