getLinkedDataFromLevel does not work if intermidate optional tables have NA

[rix133]

Sometimes tables in the hierarchy are missing and hence the getLinkedDataFromLevel seems to break eg
getLinkedDataFromLevel("BVselectMeth", "FIXED", h8, "DE", verbose = F)
returns an empty DE table while

h8LE <- getLinkedDataFromLevel("BVselectMeth", "FIXED", h8, "LE", verbose = F)

VSid <- unique(h8LE$VSid)

getLinkedDataFromLevel("VSid", VSid, h8, "DE", verbose = F)

this returns 4 rows most likely becoasue there is a empty table (FT) in between the tables
DE: 8
SD: 8
TE: 86 (NPJS,FIXED: 0-5/1-9)
VS: 89 (NPQSRSWR,NPJS: 1-4/1-13)
FT: 0
LE: 89 (NPJS,CENSUS: 1/1)
SS: 89 (CENSUS,NPJS: 1-2/1-2)
SA: 215 (NPQSRSWOR: 1-2/156-24318)
FM: 114
BV: 67971 (CENSUS,FIXED: 1-263/1-263)
VD: 1872
SL: 75
IS: 2642

The same thing happes if the intermediate table is missing the IDs like the FM