Permitting in a column only empty strings and strings that consist of whitespace characters

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WITH checks AS (SELECT ccu.table_schema, ccu.table_name, t.table_type, ccu.column_name, cc.check_clause, cc.constraint_name, 'TABLE CHECK' AS check_type, NULL AS domain_schema, NULL AS domain_name
FROM INFORMATION_SCHEMA.constraint_column_usage AS ccu INNER JOIN INFORMATION_SCHEMA.check_constraints AS cc USING (constraint_schema, constraint_name)
INNER JOIN INFORMATION_SCHEMA.tables AS t USING (table_schema, table_name)
WHERE cc.check_clause NOT LIKE '%IS NOT NULL' AND 
ccu.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 cdu.table_schema, cdu.table_name, t.table_type, cdu.column_name, cc.check_clause, cc.constraint_name, 'DOMAIN CHECK' AS check_type, cdu.domain_schema, cdu.domain_name
FROM INFORMATION_SCHEMA.column_domain_usage AS cdu INNER JOIN INFORMATION_SCHEMA.tables AS t USING (table_schema, table_name)
INNER JOIN INFORMATION_SCHEMA.domain_constraints AS dc USING (domain_schema, domain_name)
INNER JOIN INFORMATION_SCHEMA.check_constraints AS cc USING (constraint_schema, constraint_name)
WHERE t.table_type IN ('BASE TABLE','FOREIGN') AND cc.check_clause NOT LIKE '%IS NOT NULL'  AND 
cdu.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))
SELECT table_schema, table_name, table_type, column_name, check_clause, constraint_name, check_type, domain_schema, domain_name
FROM checks
WHERE check_clause~'[[:space:]]~[*]{0,1}[[:space:]]+''[\^][[]{2}[:]space[:][]]{2}[*+]{0,1}[$]'''
OR check_clause~'[[:space:]]~[*]{0,1}[[:space:]]+''[\^]\\s[*+]{0,1}[$]'
OR check_clause~'[[:space:]]~[*]{0,1}[[:space:]]+''[ ]*'''
ORDER BY table_schema, table_name,column_name;