Code block without language tag broken memos

[xinfli]

Describe the bug

I created a memo with a code block, then every time I open my memos, it shows an error Unexpected Application Error! invalid language tag: "null", I got no chance to fix it.

Steps to reproduce

1. Create a memo with content like this (Please replace "\```" with "```"):

# Title
\```
The code block
\```

3. Save the memo

Memos will show error message Unexpected Application Error! invalid language tag: "null"

The version of Memos you're using

0.19.1

Screenshots or additional context

Is there any workaround that I can fix the memo manually? thanks!