You can't have an optional 1st parameter and a required 2nd

Since the function just returns false if $container_guid isn't set, making them both optional wouldn't do anything. The real fix is probably to switch the argument order, but that is a bigger change.
get_user_sites() doesn't take a subtype arg
diagnostics_md5_dir() doesn't take a buffer arg
elgg_sql_reverse_order_by_clause() only takes a single order_by clause
Typo
removed unused and non-working function from groups plugin