BUG #4007: chr(0) doesn't work anymore

The following bug has been logged online:

Bug reference:      4007
Logged by:          Steve Clark
Email address:      sclark@netwolves.com
PostgreSQL version: 8.3.0
Operating system:   FreeBSD 6.2
Description:        chr(0) doesn't work anymore
Details:

Until 8.3.0 the following worked:
SELECT coalesce(param_value,chr(0)) from t_system_params where  param_name =
'default_unit_key';

it now fails with:
ERROR:  null character not permitted

The documentation says:
For other multibyte encodings the argument must designate a strictly ASCII
character.

NUL = 0 is a valid ascii character.