From 9710a1a2353dea5a6524bd3c52a00008ef0a11a1 Mon Sep 17 00:00:00 2001
From: Ardis Lu <ardisglu@gmail.com>
Date: Thu, 16 Oct 2025 23:52:43 -0700
Subject: [PATCH] Fix regression where `null` and `undefined` are unable to be
 denormalized

---
 src/normalization.js       |  7 ++++++-
 test/normalization.test.js | 24 ++++++++++++++++++++++++
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/src/normalization.js b/src/normalization.js
index ac7bc41..bc3cd09 100644
--- a/src/normalization.js
+++ b/src/normalization.js
@@ -389,7 +389,12 @@ export class CSVDenormalizer extends TransformStream {
           firstRow = false;
           controller.enqueue(chunk.map(f => f?.displayName ?? f.name));
         }
-        controller.enqueue(chunk.map(f => f.value instanceof Date ? f.value.toISOString() : f.value.toString()));
+        controller.enqueue(chunk.map(f => {
+          if (f.value instanceof Date) {
+            return f.value.toISOString();
+          }
+          return f.value?.toString?.() ?? '';
+        }));
       }
     });
   }
diff --git a/test/normalization.test.js b/test/normalization.test.js
index ce7bb72..d71e0ae 100644
--- a/test/normalization.test.js
+++ b/test/normalization.test.js
@@ -638,6 +638,30 @@ suite('CSVDenormalizer', { concurrency: true }, () => {
         ['a2', 'b2']
       ]));
   });
+  test('denormalizes null into empty string', { concurrency: true }, async () => {
+    await createCSVMockStream([
+      [{ name: 'a', value: null }, { name: 'b', value: null }],
+      [{ name: 'a', value: null }, { name: 'b', value: null }],
+    ])
+      .pipeThrough(new CSVDenormalizer())
+      .pipeTo(csvStreamEqualWritable([
+        ['a', 'b'],
+        ['', ''],
+        ['', '']
+      ]));
+  });
+  test('denormalizes undefined into empty string', { concurrency: true }, async () => {
+    await createCSVMockStream([
+      [{ name: 'a', value: undefined }, { name: 'b', value: undefined }],
+      [{ name: 'a', value: undefined }, { name: 'b', value: undefined }],
+    ])
+      .pipeThrough(new CSVDenormalizer())
+      .pipeTo(csvStreamEqualWritable([
+        ['a', 'b'],
+        ['', ''],
+        ['', '']
+      ]));
+  });
   test('works with instanceof', { concurrency: true }, async () => {
     const s = new CSVDenormalizer();
     deepStrictEqual(s instanceof CSVDenormalizer, true);
-- 
2.47.3