[Fix] MiraiMessageSender 修复因BotCode-Image中flashImage参数不存在导致NPE的问题;

src/main/java/net/lamgc/cgj/bot/framework/mirai/message/MiraiMessageSender.java

@@ -111,7 +111,8 @@ public class MiraiMessageSender implements MessageSender {
                 } else {
                     return MessageUtils.newChain("(参数不存在)");
                 }
-                if(code.getParameter("flashImage").equalsIgnoreCase("true")) {
+                if(Strings.nullToEmpty(code.getParameter("flashImage"))
+                        .equalsIgnoreCase("true")) {
                     return MessageUtils.flash(img);
                 } else {
                     return img;