Steps to reproduce the issue

In Joomla Tags management

1. Create a new tag:
   title: ocean
   alias: the-sea

2. In article form try to add (and then save the form) a tag that causes duplicate alias, try to add a new tag titled:
   the sea

NOTE: the article must not have any other tags just try to add a single tag, the above one

Expected result

You can add tag or you get duplicate tag alias error or some other good feedback

Actual result

You get an SQL syntax error, without any indication of what happened

System information (as much as possible)

Additional comments

Souce code doing the above is

Duplicate alias is found here
https://github.com/joomla/joomla-cms/blob/staging/libraries/src/Helper/TagsHelper.php#L260

then here you get a zero size array
https://github.com/joomla/joomla-cms/blob/staging/libraries/src/Helper/TagsHelper.php#L71

then here you get an empty SQL clause
https://github.com/joomla/joomla-cms/blob/staging/libraries/src/Helper/TagsHelper.php#L90

This is not a security issue, just an empty SQL clause, making an SQL syntax error, so i report it here

Besides the SQL syntax error
TagsHelper::addTagMapping

also has a really unhelpful return value

it does not return information to the caller of which tags were really created / mapped
it is almost a black box, if we can at least do something in B/C way , e.g. pass by reference an array that is populated with the tags that were successfully added it can become much more useful, also making possible to return error information