修复500问题

app/models/user.rb

@@ -917,6 +917,9 @@ class User < Principal
 
   # 判断是否是竞赛的主办人
   def admin_of_contest?(contest)
+    if contest.nil?
+      return false
+    end
     if ContestMember.where("user_id =? and contest_id =?", self.id, contest.id).count == 0
       return false
     end