Empty body on update generates an MySQL error #478
Description
Steps to reproduce
Generate a new project (ex: loopback example todo-list), change DB from memory objecto to MySQL, create MySQL database and config connector. Seed database with some data.
Make a PATCH request that uses updateById repository's method, with an empty body (ex: updatebyId(existingId, {}).
Current Behavior
Query fails with an SQL syntax error: "Error: ER_PARSE_ERROR: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'WHERE id='3db97b64-a616-11ec-8940-0db8a28d8117'".
This error does not occur when using a memory database.
Query sent to DB (without params) is: "UPDATE ModelA SET WHERE id=?"
Expected Behavior
A - No query should be sent to DB
B - Send correct (but useless) query to DB