add post validation

Post/post_contract.go

@@ -75,8 +75,18 @@ func GetAllPostsByUser(login string) []Post {
 	i := 1
 	n := getPostIndex(login)
 	for i < n+1 {
-		post_key := storage.Get(ctx, login+"_p_"+std.Itoa10(i)).(string)
+		post_key := storage.Get(ctx, login+"_p_"+std.Itoa10(i))
+		if post_key == nil {
+			panic("post key not found")
+		}
+
+		post_key = post_key.(string)
+
 		post := storage.Get(ctx, post_key)
+		if post == nil {
+			panic("post not found")
+		}
+
 		i++
 		postsByUser = append(postsByUser, std.Deserialize(post.([]byte)).(Post))
 	}