Forem: Http 500 Error when malformed github repo links inserted

[Slashgear]

Describe the bug

When a user want to add a github repository link in a post. If their is a / at the beginning

To Reproduce

• Goto post creation page
  
• Paste {% github /thepracticaldev/dev.to %}
  
• Try to save
  
• You will receive a 500 HTTP error

Expected behavior

It should at least send a 400 error.
It should help user with a specific message.

Screenshots


Desktop (please complete the following information):

• OS: MacOS Mojave
• Browser: Chrome
• Version: 75

[jessleenyc]

Agreed, let's send a better error message for this.