The "Server URL" field in the "Add Server Repository" dialog allow line breaks to be pasted. This shouldn't be possible. Line breaks (or any white space for that matter) can easily end up in the clipboard when copying URLs from websites.
Choose "Add Server Repository..."
Paste (using Cmd+V) an URL to the "Server URL" field that contains a (trailing or leading) line break. Such an URL (or text in general) can easily be created in a text editor.
The attached screenshot was taken after pasting an URL with a trailing line break.