Steps to reproduce:
* Enable StockRotation system preference
* Tools > Stock rotation > New rota
* Enter name "rota", save.
* Create new rota, enter name "rota" again.
* Nasty plack error

This error also occurs when updating a rota's name to an already existing rota's name.

plack-intranet-error.log:
[WARN] DBIx::Class::Storage::DBI::_dbh_execute(): DBI Exception: DBD::mysql::st execute failed: Duplicate entry 'rota' for key 'stockrotationrotas_title' at /kohadevbox/koha/Koha/Object.pm line 170


> describe stockrotationrotas;
+-------------+--------------+------+-----+---------+----------------+
| Field       | Type         | Null | Key | Default | Extra          |
+-------------+--------------+------+-----+---------+----------------+
| rota_id     | int(11)      | NO   | PRI | NULL    | auto_increment |
| title       | varchar(100) | NO   | UNI | NULL    |                |
| description | text         | NO   |     | NULL    |                |
| cyclical    | tinyint(1)   | NO   |     | 0       |                |
| active      | tinyint(1)   | NO   |     | 0       |                |
+-------------+--------------+------+-----+---------+----------------+

Seems that the title is set as unique in the database and is causing this.