From a970b95dac078baf0cc932f61125b4e8a97ff909 Mon Sep 17 00:00:00 2001
From: Yarchik <spoko.dev@gmail.com>
Date: Tue, 23 Jun 2026 01:37:48 +0100
Subject: [PATCH] fix: do not expand empty list or associative array under key
 operators

RFC 6570 section 2.3 defines a list or associative array with zero members
as undefined, so an undefined value contributes nothing to an expansion.
The key operators (?, &, ;) emitted a "name=" pair for an empty collection
anyway:

  parseTemplate('{?list}').expand({ list: [] }); // was "?list=", now ""

The non-key branch already guarded on `tmp.length`; the key branch did not.
Guard both. An empty string value stays defined and still expands to
"name=", matching RFC 6570 section 3.2.8.

The official RFC 6570 test suite's "Empty Variables" cases now pass; two
unit-test assertions that encoded the old behavior are corrected.
---
 lib/url-template.js       | 10 ++++++----
 test/url-template-test.js | 14 ++++++++++----
 2 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/lib/url-template.js b/lib/url-template.js
index 92c234b..e7405f8 100644
--- a/lib/url-template.js
+++ b/lib/url-template.js
@@ -73,10 +73,12 @@ function getValues(context, operator, key, modifier) {
           });
         }
 
-        if (isKeyOperator(operator)) {
-          result.push(encodeUnreserved(key) + '=' + tmp.join(','));
-        } else if (tmp.length !== 0) {
-          result.push(tmp.join(','));
+        if (tmp.length !== 0) {
+          if (isKeyOperator(operator)) {
+            result.push(encodeUnreserved(key) + '=' + tmp.join(','));
+          } else {
+            result.push(tmp.join(','));
+          }
         }
       }
     }
diff --git a/test/url-template-test.js b/test/url-template-test.js
index 2df84d2..e1367b9 100644
--- a/test/url-template-test.js
+++ b/test/url-template-test.js
@@ -179,15 +179,21 @@ describe('uri-template', () => {
     test('variable empty list', () => {
       assert('{/emptylist}', '');
       assert('{/emptylist*}', '');
-      assert('{?emptylist}', '?emptylist=');
+      // RFC 6570 section 2.3: a list with zero members is undefined, so a key
+      // operator must not emit a "name=" pair for it (unlike an empty string).
+      assert('{?emptylist}', '');
       assert('{?emptylist*}', '');
+      assert('{&emptylist}', '');
+      assert('{;emptylist}', '');
     });
 
     test('variable empty object', () => {
       assert('{/emptyobject}', '');
       assert('{/emptyobject*}', '');
-      assert('{?emptyobject}', '?emptyobject=');
+      assert('{?emptyobject}', '');
       assert('{?emptyobject*}', '');
+      assert('{&emptyobject}', '');
+      assert('{;emptyobject}', '');
     });
 
     test('variable undefined list item', () => {
@@ -362,8 +368,8 @@ describe('uri-template', () => {
       assert('{?var,number}', '?var=value&number=2133');
       assert('{?undef}', '');
       assert('{?emptystring}', '?emptystring=');
-      assert('{?emptylist}', '?emptylist=');
-      assert('{?emptyobject}', '?emptyobject=');
+      assert('{?emptylist}', '');
+      assert('{?emptyobject}', '');
       assert('{?undef,var,emptystring}', '?var=value&emptystring=');
     });
   });