Description
This error may take place in Apex while updating the records.
Reason
When we update the record, the record must be existing in the database – means there should be Record Id and it should be specfied.
Account a = new Account (Company = 'Tenetizer');
update a;
The above given code will throw error as Id is not mentioned.
Account a = new Account (Company = 'Tenetizer', Id='001rtjn084808058'); update a;
The above given code will work as expected!