array_nulls

This controls whether the array input parser recognizes unquoted NULL as specifying a null array element. By default, this is on, allowing array values containing null values to be entered. However, PostgreSQL versions before 8.2 did not support null values in arrays, and therefore would treat NULL as specifying a normal array element with the string value NULL. For backward compatibility with applications that require the old behavior, this variable can be turned off.

Note that it is possible to create array values containing null values even when this variable is off.