From 576180d7956b8be56f6e4f9abd322f73116f19ee Mon Sep 17 00:00:00 2001
From: yuexihuachen <2578038405@qq.com>
Date: Fri, 30 Oct 2026 21:20:22 +0800
Subject: [PATCH 1/2] Fix CSV export of missing properties (#369)

---
 src/830into.js                      |  3 +++
 test/test-csv-missing-properties.js | 21 +++++++++++++++++++++
 2 files changed, 24 insertions(+)
 create mode 100644 test/test-csv-missing-properties.js

diff --git a/src/830into.js b/src/830into.js
index 93428a74bc..ec427f304c 100755
--- a/src/830into.js
+++ b/src/830into.js
@@ -257,6 +257,9 @@ alasql.into.CSV = function (filename, opts, data, columns, cb) {
 			columns
 				.map(function (col) {
 					var s = d[col.columnid];
+					if (s === undefined) {
+						s = '';
+					}
 					// escape the character wherever it appears in the field
 					if (opt.quote !== '') {
 						s = (s + '').replace(new RegExp('\\' + opt.quote, 'g'), opt.quote + opt.quote);
diff --git a/test/test-csv-missing-properties.js b/test/test-csv-missing-properties.js
new file mode 100644
index 0000000000..31e1088658
--- /dev/null
+++ b/test/test-csv-missing-properties.js
@@ -0,0 +1,21 @@
+if (typeof exports === 'object') {
+	var assert = require('assert');
+	var alasql = require('..');
+}
+
+describe('Test 369 - CSV export with missing properties', function () {
+	it('A) Export missing properties as empty fields', function () {
+		var data = [
+			{a: 1, b: 2, c: 3, d: 4},
+			{a: 5, b: 6},
+		];
+		var res = alasql('SELECT * INTO CSV({headers:true, utf8Bom:false}) FROM ?', [data]);
+		assert.deepStrictEqual(res, '"a";"b";"c";"d"\r\n1;2;3;4\r\n5;6;;\r\n');
+	});
+
+	it('B) Preserve an explicit undefined string', function () {
+		var data = [{a: 'undefined'}];
+		var res = alasql('SELECT * INTO CSV({headers:true, utf8Bom:false}) FROM ?', [data]);
+		assert.deepStrictEqual(res, '"a"\r\n"undefined"\r\n');
+	});
+});

From 18f0d8f5b67e33dc5c8d6d4602257f3c723e35b9 Mon Sep 17 00:00:00 2001
From: yuexihuachen <2578038405@qq.com>
Date: Sun, 1 Nov 2026 09:04:05 +0800
Subject: [PATCH 2/2] Handle null CSV values as empty fields

---
 src/830into.js                      | 3 ++-
 test/test-csv-missing-properties.js | 6 ++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/830into.js b/src/830into.js
index ec427f304c..1c0362ba3c 100755
--- a/src/830into.js
+++ b/src/830into.js
@@ -257,7 +257,8 @@ alasql.into.CSV = function (filename, opts, data, columns, cb) {
 			columns
 				.map(function (col) {
 					var s = d[col.columnid];
-					if (s === undefined) {
+					// Missing properties and null values both represent empty CSV fields.
+					if (s == null) {
 						s = '';
 					}
 					// escape the character wherever it appears in the field
diff --git a/test/test-csv-missing-properties.js b/test/test-csv-missing-properties.js
index 31e1088658..d2707c2c21 100644
--- a/test/test-csv-missing-properties.js
+++ b/test/test-csv-missing-properties.js
@@ -18,4 +18,10 @@ describe('Test 369 - CSV export with missing properties', function () {
 		var res = alasql('SELECT * INTO CSV({headers:true, utf8Bom:false}) FROM ?', [data]);
 		assert.deepStrictEqual(res, '"a"\r\n"undefined"\r\n');
 	});
+
+	it('C) Export null as empty but preserve an explicit null string', function () {
+		var data = [{a: null, b: 'null'}];
+		var res = alasql('SELECT * INTO CSV({headers:true, utf8Bom:false}) FROM ?', [data]);
+		assert.deepStrictEqual(res, '"a";"b"\r\n;"null"\r\n');
+	});
 });