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Describe the bug

Checking equality of _FillValues that are NaNs in io_filenames_mod causes DART to exit.

check_attribute_value is called to check _FillValue and missing_value with the following code (r4 and r8) versions:

if ( nf90_get_att(ncFile, ncVarID, att_string, ret_spvalR4) == NF90_NOERR ) then
   if (spvalR4 /= ret_spvalR4) then
      write(msgstring,*) ' variable attribute, ', trim(att_string), ' in state', spvalR4, &
                         ' does not match ', trim(att_string), ' ', ret_spvalR4, ' in ', trim(filename)
      call error_handler(E_ERR, 'check_attribute_value_r4', msgstring, source)
   endif
endif

If _FillValue is NaN then (spvalR4 /= ret_spvalR4) is always true.

Error Message

 ERROR FROM:

  source : io_filenames_mod.f90
  routine: check_attribute_value_r4
  message:   variable attribute, _FillValue in state            NaN  does not match _FillValue             NaN  in /glade/work/gharamti/wrfhydro_dart/florence/initial_ens/hybrid/init_ens/member_000/HYDRO_RST.2018-08-01_00:00_DOMAIN1

Which model(s) are you working with?

Found with wrf-hydro, will effect any netcdf variable that has a missing or fill value attribute that is NaN.

Version of DART

9.12 (been there since at least 2016 though)

Have you modified the DART code?

No

Note to myself: You can test for NaNs before testing /=, but why do we even have to check the missing/fill value attribute is the same? State vs. netcdf file. Input vs. Output. Query the missing/fill value before you write?