diff --git a/core/DbConnectionWrapper.php b/core/DbConnectionWrapper.php
index 2b25128ab..6f352bc2e 100644
--- a/core/DbConnectionWrapper.php
+++ b/core/DbConnectionWrapper.php
@@ -56,12 +56,29 @@ class DbConnectionWrapper
 	}
 
 	/**
-	 * Use this to register a mock that will handle {@see mysqli::query()}
+	 * mysqli object is really hard to mock as it contains lots of attributes & methods ! Thought we need to mock it to test transactions !
 	 *
-	 * @param \mysqli|null $oMysqli
+	 * To solve this, a new attribute exists and is only used in specific use cases, so there are just few things to mock.
+	 *
+	 * This object adds more readability than previous model with 2 attributes in {@see CMDBSource}.
+	 *
+	 * @used-by \CMDBSource
+	 *
+	 * @since 3.0.0 N°4325 Object creation
+	 *          This wrapper handles the 2 {@mysqli myqsli} attributes that were previously in {@see CMDBSource}
+	 *          To allow testing we added a second mysqli object (N°3513 in 2.7.5) and code became a bit confusing :/
+	 *          With this wrapper everything is in the same place, and we can express the intention more clearly !
+	 * @since 3.1.0-4 N°6848 backport of restoring cnx on null parameter value
 	 */
-	public static function SetDbConnectionMockForQuery(?mysqli $oMysqli): void
+
+	public static function SetDbConnectionMockForQuery(?mysqli $oMysqli = null): void
 	{
-		static::$oDbCnxMockableForQuery = $oMysqli;
+		if (is_null($oMysqli)) {
+			// Reset to standard connection
+			static::$oDbCnxMockableForQuery = static::$oDbCnxStandard;
+		}
+		else {
+			static::$oDbCnxMockableForQuery = $oMysqli;
+		}
 	}
 }
\ No newline at end of file
diff --git a/tests/php-unit-tests/unitary-tests/core/CMDBSource/TransactionsTest.php b/tests/php-unit-tests/unitary-tests/core/CMDBSource/TransactionsTest.php
index 5ee8ca63a..b30bca12a 100644
--- a/tests/php-unit-tests/unitary-tests/core/CMDBSource/TransactionsTest.php
+++ b/tests/php-unit-tests/unitary-tests/core/CMDBSource/TransactionsTest.php
@@ -276,6 +276,7 @@ class TransactionsTest extends ItopTestCase
 	protected function tearDown(): void
 	{
 		try {
+			DbConnectionWrapper::SetDbConnectionMockForQuery(); // Else will throw error on PHP 8.1+ (see N°6848)
 			parent::tearDown();
 		}
 		catch (MySQLTransactionNotClosedException $e) {