fix(vastbase): tolerate NULL columns in index metadata scan

agents/drivers/vastbase-go/vastbase_metadata.go

@@ -657,17 +657,19 @@ func (s *server) listIndexes(schema, table string) ([]indexInfo, error) {
 	defer rows.Close()
 	catalogIndexes := []vastbaseCatalogIndex{}
 	attributes := map[int]string{}
+	// UNION ALL 双分支各列可空性无法保证（Vastbase G100 在某些表/索引形态下会返回 NULL），
+	// 统一用可空类型扫描以容错 NULL，避免 convertAssign 崩溃（#5602）。
 	for rows.Next() {
-		var rowKind, attributeNumber int
-		var name, kind, columnNumbers, column string
+		var rowKind, attributeNumber sql.NullInt64
+		var name, kind, columnNumbers, column sql.NullString
 		var unique, primary bool
 		if err := rows.Scan(&rowKind, &name, &kind, &unique, &primary, &columnNumbers, &attributeNumber, &column); err != nil {
 			return nil, err
 		}
-		if rowKind == 0 {
-			catalogIndexes = append(catalogIndexes, vastbaseCatalogIndex{name: name, indexType: kind, unique: unique, primary: primary, columnNumbers: columnNumbers})
-		} else if attributeNumber > 0 && column != "" {
-			attributes[attributeNumber] = column
+		if rowKind.Int64 == 0 {
+			catalogIndexes = append(catalogIndexes, vastbaseCatalogIndex{name: name.String, indexType: kind.String, unique: unique, primary: primary, columnNumbers: columnNumbers.String})
+		} else if attributeNumber.Int64 > 0 && column.String != "" {
+			attributes[int(attributeNumber.Int64)] = column.String
 		}
 	}
 	if err := rows.Err(); err != nil {

agents/drivers/vastbase-go/vastbase_metadata_test.go

@@ -47,6 +47,43 @@ func TestVastbaseListIndexesMapsCatalogVectorsInOneQuery(t *testing.T) {
 	assertVastbaseIndex(t, indexes[1], "orders_pkey", []string{"id", "tenant_id"}, true, true, "btree")
 }
 
+// TestVastbaseListIndexesToleratesNullColumnName 复刻 #5602：Vastbase G100 在 UNION ALL
+// 索引查询中对 column_name（column index 7）返回 NULL，裸 string 扫描会报
+// "converting NULL to string is unsupported"。修复后用 sql.NullString 容错，NULL 行被跳过不崩。
+func TestVastbaseListIndexesToleratesNullColumnName(t *testing.T) {
+	state := &vastbaseIndexMetadataTestState{
+		rows: [][]driver.Value{
+			// 分支1（row_kind=0）的 column_name 占位列也可能为 NULL，不应影响索引元数据解析。
+			{int64(0), "orders_pkey", "btree", true, true, "1 3", int64(0), nil},
+			{int64(1), "", "", false, false, "", int64(1), "id"},
+			// 模拟 Vastbase 对某 attribute 行的 column_name 返回 NULL，该行应被跳过。
+			{int64(1), "", "", false, false, "", int64(2), nil},
+			{int64(1), "", "", false, false, "", int64(3), "code"},
+		},
+	}
+	driverName := fmt.Sprintf("vastbase-index-null-%d", vastbaseIndexMetadataDriverSequence.Add(1))
+	sql.Register(driverName, &vastbaseIndexMetadataTestDriver{state: state})
+	db, err := sql.Open(driverName, "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { _ = db.Close() })
+
+	server := newServer()
+	server.db = db
+	server.mode.postgresCatalog = true
+	indexes, err := server.listIndexes("app", "orders")
+	if err != nil {
+		t.Fatalf("listIndexes should tolerate NULL column_name, got error: %v", err)
+	}
+	// orders_pkey 的 indkey 为 "1 3"，对应 id(1) 和 code(3)；attribute 2 的 NULL 行被跳过，
+	// 但 id 与 code 仍可解析，因此索引应正常返回。
+	if len(indexes) != 1 {
+		t.Fatalf("listIndexes returned %d indexes, want 1: %+v", len(indexes), indexes)
+	}
+	assertVastbaseIndex(t, indexes[0], "orders_pkey", []string{"id", "code"}, true, true, "btree")
+}
+
 func TestParseVastbaseAttributeNumbersSupportsCatalogRepresentations(t *testing.T) {
 	for _, test := range []struct {
 		raw      string
@@ -80,6 +117,8 @@ var vastbaseIndexMetadataDriverSequence atomic.Uint64
 type vastbaseIndexMetadataTestState struct {
 	queryCount int
 	query      string
+	// rows 为非空时覆盖默认返回数据，用于注入 NULL 等边界场景。
+	rows [][]driver.Value
 }
 
 type vastbaseIndexMetadataTestDriver struct {
@@ -103,16 +142,18 @@ func (*vastbaseIndexMetadataTestConn) Begin() (driver.Tx, error) { return nil, d
 func (conn *vastbaseIndexMetadataTestConn) QueryContext(_ context.Context, query string, _ []driver.NamedValue) (driver.Rows, error) {
 	conn.state.queryCount++
 	conn.state.query = query
-	return &vastbaseIndexMetadataTestRows{
-		rows: [][]driver.Value{
+	rows := conn.state.rows
+	if rows == nil {
+		rows = [][]driver.Value{
 			{int64(0), "orders_code_idx", "btree", true, false, "3 2", int64(0), ""},
 			{int64(0), "orders_expression_idx", "btree", false, false, "0 2", int64(0), ""},
 			{int64(0), "orders_pkey", "btree", true, true, "1 2", int64(0), ""},
 			{int64(1), "", "", false, false, "", int64(1), "id"},
 			{int64(1), "", "", false, false, "", int64(2), "tenant_id"},
 			{int64(1), "", "", false, false, "", int64(3), "code"},
-		},
-	}, nil
+		}
+	}
+	return &vastbaseIndexMetadataTestRows{rows: rows}, nil
 }
 
 type vastbaseIndexMetadataTestRows struct {