When a new column is added to an existing table, the value of these columns in existing records is initialized to NULL. This improves the performance of Database Reorganization and limits the disk space required for the reorganized table.

In most cases, the value of these columns returned to the application appears to be spaces (String attribute) or zeros (Number attribute). One exception to this is if you use the new column in a Profile, then a value of NULL in a String column is sorted before spaces. This might result in an unexpected behavior in the order or selection of records while reading via Profiles. If you suspect this might be an issue, then you would need to create a process to explicitly update the columns in the existing records with spaces or zeros.