We imported about 20000 Postal codes in our system, and almost all of them have some information in the /street/ field. However, we found out that the information in /Street/ field are not correct, and we need to delete information in the /Street/ field for all 20000 postal codes. The problem is, when we try to import the same postal code but with an empty /Street/ field, the system create new records instead of updating existing records. What should we do?