Specifying variables in outputfile

[fplpml]

Hello,
When I have created a setup at L4 with non-benthic fabm.yaml file which had all bilogical modules switched off (use: false) I wanted to save only a handful of variables into the output file. An error was rised at initialisation of the run as follows:
bL2_c_sms_tot_calculator_result benthic calcite c_sms_tot_calculator result
Using Eulerian solver
Using euler_forward()
done.
Using constant fabm/input/mole_fraction_of_carbon_dioxide_in_air= 385.00000000000000
Using constant fabm/input/absorption_of_silt= 7.0000000000000007E-002
Using constant fabm/input/bottom_stress= 0.0000000000000000
FATAL ERROR: create_load_commands: Variable particulate_organic_absorption_coefficient_calculator/result is marked for preloading but has no valid data.
Note: The following floating-point exceptions are signalling: IEEE_DENORMAL
STOP 1

If I include bottom values saving source: * into the gotm.yaml file this error doesnt appear and the simulation completes correctly.

A similar error occours with a setup including benthic system and all biology switched on. Here bottom values need to be saved including all variables (source: *) to let the run complete correctly otherwise similar error would appear:

Using constant fabm/input/absorption_of_silt= 7.0000000000000007E-002
Using constant fabm/input/bottom_stress= 0.0000000000000000
FATAL ERROR: create_load_commands: Variable total_bioturbation_activity_at_bottom_calculator/result is marked for preloading but has no valid data.
Note: The following floating-point exceptions are signalling: IEEE_DENORMAL
STOP 1

[jimc101]

Not yet sure whether this is an ERSEM issue, a FABM issue or a problem with the config files. Whatever, the error message feels a little cryptic given the change that causes it. @jornbr - do you have a take on the FABM question?