From 655a5c8e47314086e589b3e67c7b167c68df96b6 Mon Sep 17 00:00:00 2001
From: Vladimir Vagaytsev <vladimir.vagaitsev@gmail.com>
Date: Wed, 12 Jul 2023 13:42:38 +0200
Subject: [PATCH] fix(template): allow `null` as a valid argument in helper
 functions

---
 core/src/template-string/functions.ts |  6 ++++--
 core/test/unit/src/template-string.ts | 14 ++++++++++++++
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/core/src/template-string/functions.ts b/core/src/template-string/functions.ts
index 7738c0c24e..4b4241c4b0 100644
--- a/core/src/template-string/functions.ts
+++ b/core/src/template-string/functions.ts
@@ -479,11 +479,13 @@ export function callHelperFunction({
   const resolvedArgs: any[] = []
 
   for (const arg of args) {
-    if (arg._error) {
+    // arg can be null here because some helpers allow nulls as valid args
+    if (arg && arg._error) {
       return arg
     }
 
-    if (arg && arg.resolved) {
+    // allow nulls as valid arg values
+    if (arg && arg.resolved !== undefined) {
       resolvedArgs.push(arg.resolved)
     } else {
       resolvedArgs.push(arg)
diff --git a/core/test/unit/src/template-string.ts b/core/test/unit/src/template-string.ts
index bfb0c55e4b..57b56b31fa 100644
--- a/core/test/unit/src/template-string.ts
+++ b/core/test/unit/src/template-string.ts
@@ -1107,6 +1107,20 @@ describe("resolveTemplateString", () => {
       })
     })
 
+    context("isEmpty", () => {
+      context("allows nulls", () => {
+        it("resolves null as 'true'", () => {
+          const res = resolveTemplateString("${isEmpty(null)}", new TestContext({}))
+          expect(res).to.be.true
+        })
+
+        it("resolves references to null as 'true'", () => {
+          const res = resolveTemplateString("${isEmpty(a)}", new TestContext({ a: null }))
+          expect(res).to.be.true
+        })
+      })
+    })
+
     context("slice", () => {
       it("allows numeric indices", () => {
         const res = resolveTemplateString("${slice(foo, 0, 3)}", new TestContext({ foo: "abcdef" }))