diff --git a/web/src/components/RealtimeTable/contexts/RealtimeContext.js b/web/src/components/RealtimeTable/contexts/RealtimeContext.js
index c56e894..cce0cb6 100644
--- a/web/src/components/RealtimeTable/contexts/RealtimeContext.js
+++ b/web/src/components/RealtimeTable/contexts/RealtimeContext.js
@@ -1,6 +1,7 @@
 import { createContext, useCallback, useContext, useEffect, useMemo, useRef, useState, useSyncExternalStore } from 'react';
 import { toast } from 'react-toastify';
 import { useWebSocket } from '../hooks/useWebSocket';
+import { buildCellUpdatedMessage } from '../utils/messageUtils';
 import { getRowId } from '../utils/rowUtils';
 
 const RealtimeActionsContext = createContext(null);
@@ -310,15 +311,7 @@ export const RealtimeProvider = ({ children, formId, sheetName, direction, year,
 
 			const lineId = getRowId(row);
 			const columnKey = getColumnRequestKey(column);
-			const message = {
-				event: 'cell_updated',
-				data: {
-					line_id: lineId,
-					line_id_code: row.id,
-					column: columnKey,
-					value: value,
-				},
-			};
+			const message = buildCellUpdatedMessage({ lineId, lineIdCode: row.id, column: columnKey, value });
 			const sent = sendMessage(message);
 
 			if (!sent) {
diff --git a/web/src/components/RealtimeTable/utils/messageUtils.js b/web/src/components/RealtimeTable/utils/messageUtils.js
new file mode 100644
index 0000000..5e305ed
--- /dev/null
+++ b/web/src/components/RealtimeTable/utils/messageUtils.js
@@ -0,0 +1,10 @@
+// value всегда присутствует: сервер читает event_data["value"], AURORA-1848 D5.2
+export const buildCellUpdatedMessage = ({ lineId, lineIdCode, column, value }) => ({
+	event: 'cell_updated',
+	data: {
+		line_id: lineId,
+		line_id_code: lineIdCode,
+		column,
+		value: value === undefined ? null : value,
+	},
+});
diff --git a/web/src/components/RealtimeTable/utils/messageUtils.test.js b/web/src/components/RealtimeTable/utils/messageUtils.test.js
new file mode 100644
index 0000000..2e7bb6c
--- /dev/null
+++ b/web/src/components/RealtimeTable/utils/messageUtils.test.js
@@ -0,0 +1,17 @@
+import assert from 'node:assert/strict';
+import { test } from 'node:test';
+import { buildCellUpdatedMessage } from './messageUtils.js';
+
+const msg = (value) => buildCellUpdatedMessage({ lineId: 1, lineIdCode: '0.1', column: 'q1.m1', value });
+
+test('buildCellUpdatedMessage: undefined → null, ключ value есть после JSON.stringify', () => {
+	const m = msg(undefined);
+	assert.deepEqual(m, { event: 'cell_updated', data: { line_id: 1, line_id_code: '0.1', column: 'q1.m1', value: null } });
+	assert.match(JSON.stringify(m), /"value":null/);
+});
+
+test('buildCellUpdatedMessage: прочие значения не меняются', () => {
+	for (const v of [null, 0, '', '1.5', 42, 'текст']) {
+		assert.equal(msg(v).data.value, v);
+	}
+});