fix error_str creation

bot/src/cogs/projects.py

@@ -363,7 +363,7 @@ async def share(
         github_names_str = 'no members' if not len(github_accounts) else ', '.join(map(lambda github: f'```{github[0].github}```', github_accounts))
         no_github_str = '' if not len(no_github) else 'no GitHub linked: ' + ', '.join(map(lambda member: f'```{member}```', no_github))
         invalid_github_str = '' if not len(invalid_github) else 'invalid GitHub usernames: ' + ', '.join(map(lambda member: f'```{member}```', invalid_github))
-        error_str = ', '.join([no_github_str, invalid_github_str])
+        error_str = ', '.join(filter(None, [no_github_str, invalid_github_str]))
 
         await interaction.send(f"Project shared to {github_names_str} {f'({error_str})' if error_str else ''}")