Fix TemplateService helpers initialization

template/html/option.go

@@ -33,6 +33,9 @@ func WithDefaultHelpers() OptionFunc {
 // to expose the default helpers
 func WithHelper(name string, fn interface{}) OptionFunc {
 	return func(opts *Options) {
+		if opts.Helpers == nil {
+			opts.Helpers = make(template.FuncMap)
+		}
 		opts.Helpers[name] = fn
 	}
 }