Comments by SleepyCrat (Top 1 by date)

This is just a a question, but in your customer object that you are creating at first you are not setting the field 'Id', but you are setting it in the customer object you are creating in the CreateList() function. Also in the comparison statement you are using to get the 'filter' object
the second part of your statement is "l.Id != customer.Id'. Did you perhaps mean to set the Id field the same in both objects and use 'l.Id == customer.Id'?