Incorrect check of NULLs

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WITH expressions AS (select 
n.nspname as schema,
c.relname || '.' || o.conname as name, 
substring(pg_get_constraintdef(o.oid),7) as expression,
'TABLE CHECK' AS type
from pg_constraint o inner join pg_class c on c.oid = o.conrelid
inner join pg_namespace n on n.oid=c.relnamespace
where o.contype ='c'
and n.nspname not in (select schema_name
from information_schema.schemata
where schema_name<>'public' and
schema_owner='postgres' and schema_name is not null)
union select n.nspname as schema,
t.typname || '.' || o.conname as name, 
substring(pg_get_constraintdef(o.oid),7) as expression,
'DOMAIN CHECK' AS type
from pg_constraint o inner join pg_type t on t.oid = o.contypid
inner join pg_namespace n on n.oid=t.typnamespace
where o.contype ='c' and n.nspname not in (select schema_name
from information_schema.schemata
where schema_name<>'public' and
schema_owner='postgres' and schema_name is not null)
UNION SELECT trigger_schema, event_object_table || '.' || trigger_name, action_condition, 'TRIGGER WHEN' AS type
FROM INFORMATION_SCHEMA.triggers
WHERE action_condition IS NOT NULL
UNION SELECT schemaname, tablename || '.' || rulename, definition, 'RULE WHERE' AS type
FROM pg_catalog.pg_rules
WHERE schemaname NOT IN (SELECT schema_name
FROM INFORMATION_SCHEMA.schemata
WHERE schema_name<>'public' AND
schema_owner='postgres' AND schema_name IS NOT NULL)
UNION SELECT table_schema, table_name, view_definition, type
FROM (SELECT  table_schema, table_name, regexp_replace(view_definition,'[\r\n]','<br>','g') AS view_definition, 'VIEW SUBQUERY' AS type
FROM information_schema.views
WHERE table_schema NOT IN (SELECT schema_name
FROM INFORMATION_SCHEMA.schemata
WHERE schema_name<>'public' AND
schema_owner='postgres' AND schema_name IS NOT NULL)
UNION SELECT schemaname, matviewname, regexp_replace(definition,'[\r\n]','<br>','g') AS definition, 'MATERIALIZED VIEW SUBQUERY' AS type
FROM pg_catalog.pg_matviews) AS foo
WHERE view_definition ~*'^.+([[:space:]]+where[[:space:]]+|[[:space:]]+having[[:space:]]+).+$'
UNION SELECT pg_namespace.nspname AS routine_schema,  pg_proc.proname || '(' || pg_get_function_identity_arguments(pg_proc.oid)  || ')' AS routine_name,  regexp_replace(pg_proc.prosrc,'[\r\n]','<br>','g')  AS routine_src, 'ROUTINE BODY' AS type
FROM pg_catalog.pg_proc, pg_catalog.pg_namespace
WHERE pg_proc.pronamespace = pg_namespace.oid AND
pg_proc.proname NOT IN ('f_assume_you_must_use_files', 'f_check_format_comma_separated_list', 'f_check_password', 'f_default_value_with_no_match') AND 
pg_namespace.nspname NOT IN (SELECT schema_name
FROM INFORMATION_SCHEMA.schemata
WHERE schema_name<>'public' AND
schema_owner='postgres' AND schema_name IS NOT NULL) AND NOT EXISTS (SELECT 1
FROM pg_catalog.pg_depend d 
WHERE EXISTS (SELECT 1 FROM pg_catalog.pg_extension e WHERE d.refobjid=e.oid) AND
d.objid=pg_proc.oid))
SELECT schema, name AS object_identifier, type AS object_type, expression AS suspected_expression
FROM expressions
WHERE expression ~*'^.*((<>|!=)[[:space:]]*NULL([[:space:]]+|::)|(?<!update[^;]*)=[[:space:]]*NULL([[:space:]]+|::)|NULL([[:space:]]*|::)(<>|!=)|NULL([[:space:]]*|::)=).*$'
ORDER BY schema, type, name;