fix: for throws undefined var with a null value with strictVariables

src/context/context.ts

@@ -79,8 +79,9 @@ export class Context {
   public * _getFromScope (scope: unknown, paths: PropertyKey[] | string): IterableIterator<unknown> {
     if (isString(paths)) paths = paths.split('.')
     for (let i = 0; i < paths.length; i++) {
+      const previousScope = scope
       scope = yield readProperty(scope as object, paths[i], this.ownPropertyOnly)
-      if (isNil(scope) && this.strictVariables) {
+      if (this.strictVariables && isNil(scope) && !definedProperty(previousScope as object, paths[i], this.ownPropertyOnly)) {
         throw new InternalUndefinedVariableError((paths as string[]).slice(0, i + 1).join!('.'))
       }
     }
@@ -105,6 +106,13 @@ export class Context {
   }
 }
 
+export function definedProperty (obj: Scope, key: PropertyKey, ownPropertyOnly: boolean) {
+  obj = toLiquid(obj)
+  if (isNil(obj)) return false
+  if (isArray(obj)) return false
+  return ownPropertyOnly && Object.hasOwnProperty.call(obj, key)
+}
+
 export function readProperty (obj: Scope, key: PropertyKey, ownPropertyOnly: boolean) {
   obj = toLiquid(obj)
   if (isNil(obj)) return obj

test/integration/tags/for.spec.ts

@@ -59,6 +59,12 @@ describe('tags/for', function () {
     const html = await liquid.parseAndRender(src, scope)
     return expect(html).toBe('str-"string"-string')
   })
+  it('should not report undefined variable on null value', async function () {
+    const engine = new Liquid({ strictVariables: true })
+    const src = '{% assign hello = "hello,world" | split: "," | concat: null %}{% for i in hello %}{{ i }},{% endfor %}'
+    const html = await engine.parseAndRender(src, scope)
+    return expect(html).toBe('hello,world,,')
+  })
   describe('illegal', function () {
     it('should reject when for not closed', function () {
       const src = '{%for c in alpha%}{{c}}'