Overloading may cause runtime error

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WITH routines AS (SELECT 
  pg_proc.oid AS routine_oid,
  pg_namespace.nspname AS routine_schema, 
  pg_proc.proname AS routine_name,    
  CASE WHEN pg_proc.prokind='f' THEN 'FUNCTION'
  WHEN pg_proc.prokind='p' THEN 'PROCEDURE'
  WHEN pg_proc.prokind='a' THEN 'AGGREGATE FUNCTION'
  WHEN pg_proc.prokind='w' THEN 'WINDOW FUNCTION' END AS routine_type,
  proargtypes[0:(pronargs - pronargdefaults)-1] AS parameters_without_defaults,
  pg_get_function_arguments(pg_proc.oid) AS parameters
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))
SELECT  a.routine_type AS routine_type, a.routine_schema AS r1_schema, a.routine_name AS r1_routine_name, a.parameters AS r1_params,
b.routine_schema AS r2_schema, b.routine_name AS r2_routine_name, b.parameters AS r2_params
FROM routines AS a, routines AS b
WHERE a.routine_oid>b.routine_oid AND
a.routine_schema=b.routine_schema AND
a.routine_name=b.routine_name AND
a.parameters_without_defaults=b.parameters_without_defaults AND
a.routine_type=b.routine_type
ORDER BY a.routine_schema, a.routine_name, b.routine_schema, b.routine_name;