SQL query to count but producing an error : I am writing a query to find the number of ED visits that were discharged from non-ED units.
The column dep.ADT_UNIT_TYPE_C column stores 1 if the unit was an ED unit.
NULL values are non-ED units in this query.

Is this correct to produce this number?

COUNT ( CASE WHEN 
dep.ADT_UNIT_TYPE_C is NULL or dep.ADT_UNIT_TYPE_C <> 1
ELSE NULL
END )