Error: MISSING_ARGUMENT, Id not specified in an update call: []

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!