Some data modification functions return a value and some not

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WITH routines AS (SELECT 
  pg_namespace.nspname AS routine_schema, 
  pg_proc.proname AS routine_name, 
  pg_get_function_identity_arguments(pg_proc.oid) AS parameters,
  pg_language.lanname AS language,
  pg_type.typname AS return_type,
  regexp_replace(pg_get_functiondef(pg_proc.oid),'[\r\n]','<br>','g')  AS routine_src
FROM 
  pg_catalog.pg_proc, 
  pg_catalog.pg_namespace,
  pg_catalog.pg_language,
  pg_catalog.pg_type
WHERE 
  pg_proc.pronamespace = pg_namespace.oid 
  AND pg_proc.prolang = pg_language.oid
  AND pg_type.oid=pg_proc.prorettype  
  AND pg_language.lanname in ('plpgsql', 'sql')
  AND pg_type.typname<>'trigger' 
  AND pg_get_functiondef(pg_proc.oid)~*'(insert[[:space:]]+into|(?<!for[[:space:]]+)update|delete[[:space:]]+from|merge)[[:space:]]'
  AND pg_proc.prokind='f' 
  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))
SELECT routine_schema, routine_name, parameters, return_type, language, routine_src
FROM routines
WHERE EXISTS (SELECT * FROM routines WHERE return_type='void')
AND EXISTS (SELECT * FROM routines WHERE return_type<>'void')
ORDER BY routine_schema, routine_name, parameters;