[FIX] fix some issues with t-out with falsy values, and with default value

src/runtime/template_helpers.ts

@@ -129,9 +129,9 @@ class LazyValue {
 /*
  * Safely outputs `value` as a block depending on the nature of `value`
  */
-export function safeOutput(value: any): ReturnType<typeof toggler> {
-  if (!value) {
-    return value;
+export function safeOutput(value: any, defaultValue?: any): ReturnType<typeof toggler> {
+  if (value === undefined) {
+    return defaultValue ? toggler("default", defaultValue) : toggler("undefined", text(""));
   }
   let safeKey;
   let block;