# Handling NULL values

NULL values in your source data can present problems. There are also times when you might want to write NULL to a target field.

NULL values are normally only relevant with SQL style source or target systems. You will not get a NULL value when reading a text (CSV) file, although you may get an empty string.

## Testing for NULL

Inaport supplies a special function for testing for NULL values in a field: isnull() will return TRUE if the field is NULL.

## Writing a NULL value

If you want to set a target field to NULL, set the source field to the value "NULL_VALUE" (case sensitive). When generating the SQL to write to the target system, NULL will be used as the value of the target field.

## Matching against NULL

When building the in-memory indexes for standard and fuzzy matching, a NULL value in the target field will be mapped to the string "NULL_VALUE". this means that you can match against NULL fields in the target by using the string "NULL_VALUE" as the match value.