Issue with AET01 assertion for DTHFL

[barnett11]

Issue:
Currently aet01 is causing an assertion error if ADSL.DTHFL is missing. Unfortunately this is the standard for DTHFL to either be "Y" or NA so this is regularly failing.

Proposed Solution:
Similar to DCSREAS pre-processing, add the below to aet01 pre-processing,

adam_db$adsl <- adam_db$adsl %>% mutate(DTHFL= reformat(.data$DTHFL, 
        missing_rule))