fix: handle potential null values in decode parameters and improve message parsing logic

Author: HaloWang

lib/model/message.dart

@@ -271,5 +271,8 @@ extension BatchMessage on Message {
 
   List<String> get contentAndTails => content.split(Config.userMsgModifierSep);
 
+  // TODO: 应该作为 msg 的内存值, 不要在 Build 方法中调用, 如果 msg 没有这个值, 调用并解析, 如果 msg 这个值不为空, 直接取值
+
+  // TODO: @wangce 检查一下什么时候这个方法会被传递空值
   List<SamplerAndPenaltyParam> get parsedDecodeParams => SamplerAndPenaltyParamWithString.fromRawDecodeParams(rawDecodeParams ?? "");
 }

lib/widgets/chat/batch_message_content.dart

@@ -178,6 +178,7 @@ class _BatchMessageContentState extends ConsumerState<BatchMessageContent> {
 
 class _MarkdownBody extends ConsumerWidget {
   final String data;
+
   final SamplerAndPenaltyParam? decodeParam;
 
   const _MarkdownBody({required this.data, this.decodeParam});
@@ -206,7 +207,7 @@ class _MarkdownBody extends ConsumerWidget {
 
     final s = S.of(context);
 
-    final displayText = s.decode_param + s.hyphen + decodeParam!.displayName;
+    final displayText = s.decode_param + s.hyphen + (decodeParam?.displayName ?? "unknown");
 
     final Widget? decodeParamWidget = decodeParam != null
         ? Align(