From becbd14892e3cbb365358a156da928abba05921a Mon Sep 17 00:00:00 2001
From: Robert Yokota <rayokota@gmail.com>
Date: Sun, 24 May 2026 11:46:50 -0700
Subject: [PATCH] Preserve JSON null when indexing into an array

---
 src/jsonata/Jsonata.cpp | 23 +++++++++++++++--------
 test/NullSafetyTest.cpp | 10 ++++++++++
 2 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/src/jsonata/Jsonata.cpp b/src/jsonata/Jsonata.cpp
index 8dc42c1..fae86a0 100644
--- a/src/jsonata/Jsonata.cpp
+++ b/src/jsonata/Jsonata.cpp
@@ -1868,6 +1868,9 @@ std::any Jsonata::evaluateFilter(std::shared_ptr<Parser::Symbol> predicate,
         if (inputSequence.tupleStream) {
             results.tupleStream = true;
         }
+    } else if (!input.has_value()) {
+        // undefined input yields undefined output; skip filtering entirely
+        inputSequence = Utils::createSequence();
     } else if (!Utils::isArray(input)) {
         inputSequence = Utils::createSequence(input);
     } else {
@@ -1893,14 +1896,18 @@ std::any Jsonata::evaluateFilter(std::shared_ptr<Parser::Symbol> predicate,
             // ((List)input).get(index) : null;
             if (index >= 0 && index < static_cast<int64_t>(inputSequence.size())) {
                 auto item = inputSequence[index];
-                // Follow Java exactly: only add if item != null
-                if (item.has_value()) {
-                    // Java reference line 505: if(item instanceof List)
-                    if (Utils::isArray(item)) {
-                        results = Utils::arrayify(item);
-                    } else {
-                        results.push_back(item);
-                    }
+                // Preserve JSON null at this index (vs. out-of-bounds, which is
+                // undefined). An empty std::any here means the element was a
+                // JSON null; promote it to NULL_VALUE so downstream
+                // has_value() filtering keeps it.
+                if (!item.has_value()) {
+                    item = Utils::NULL_VALUE;
+                }
+                // Java reference line 505: if(item instanceof List)
+                if (Utils::isArray(item)) {
+                    results = Utils::arrayify(item);
+                } else {
+                    results.push_back(item);
                 }
             }
         } catch (const std::bad_any_cast&) {
diff --git a/test/NullSafetyTest.cpp b/test/NullSafetyTest.cpp
index a6e0b1c..04aeb81 100644
--- a/test/NullSafetyTest.cpp
+++ b/test/NullSafetyTest.cpp
@@ -69,6 +69,16 @@ TEST_F(NullSafetyTest, testSingleNull) {
     EXPECT_EQ(result.get<int>(), 1);
 }
 
+TEST_F(NullSafetyTest, testArrayIndexPreservesNull) {
+    // Indexing into an array element that is JSON null must yield null,
+    // not be filtered out as if it were undefined.
+    auto data = nlohmann::ordered_json::parse(
+        R"({"data": [[1, null, 3], [2, null, 4], [3, null, 5]]})");
+    auto result = Jsonata("[$map(data, function($row) { $row[1] })]").evaluate(data);
+    auto expected = nlohmann::ordered_json::parse("[null, null, null]");
+    EXPECT_EQ(result, expected);
+}
+
 TEST_F(NullSafetyTest, testFilterNullLookup) {
     nlohmann::ordered_json arrayData = nlohmann::ordered_json::array({
         nlohmann::ordered_json::object({{"content", "some"}}),