ORA-48415: Syntax error found in string [] at column []

with fil as (
   select
      case when platform_name like 'Microsoft Windows %' then '\' else '/' end separator
   from
      v$database
)
select
   null
from
   fil                                          cross join
   v$diag_trace_file_contents trc                     join
   v$diag_info                inf on inf.value = trc.adr_home || fil.separator || 'trace' || fil.separator || trc.trace_filename
where
   inf.name = 'Default Trace File';