Generic type is not support in entity?

[taosimple]

build Error:

[SEVERE] floor_generator on lib/db/db.dart:

Column type is not supported for T?.
package:easy_table/bean/chat_message.dart:21:6
   ╷
21 │   T? content;
   │      ^^^^^^^
   ╵

Code bean

abstract class Message<T> {
  int time;
  String? role;
  T? content;  
}

@JsonSerializable()
@Entity(
  tableName: TABLE_CHAT_MESSAGE,
  indices: [
    Index(value: ['pageUid'])
  ],
)
class TextMessage extends Message<String>{
  List<ToolCall>? tool_calls;
}

Code db

@Database(version: DB_VERSION, entities: [TextMessage])
@TypeConverters([])
abstract class DB extends FloorDatabase {
....
}