I have the following domain:

dom_input_code CHAR(1) CHECK (VALUE IN ('C', 'D'))

I have a table with the input_code column that uses the domain as the
data type. Neither the domain nor the table DDL forbid NULL in that
column, ie. NULL should be allowed.

However when I try to insert a new row where the value of that column
is NULL, I get a validation error. Similarly when I try to set the
value of the column to NULL I get a validation error.

I tried to drop the column, and re-add it using a simple type (ie. not
the domain. I could add/modify rows and set the column value to NULL
without any problem.

Then I modified the column to use the domain - and again NULLs could
not be inserted/update for the column. I checked and re-checked and
neither the domain nor the column were defined as NOT NULL.

I use FB 1.5.2 SuperServer and Database Workbench 2.8.5 as development
front-end.

Is this a bug in Firebird? Is this a "feature" of domains? Is there
any workaround?

Thanks,

Eyal Zvi