lägg till ett villkor i WHERE
sats för att utesluta rader med alla värden tom sträng
select stuff((
select '; ' + ([FIELD_1] + [FIELD_2] + [...] + [FIELD_N])
from [TABLE] t1
where t1.[ID] = t2.[ID]
and [FIELD_1] + [FIELD_2] + [...] + [FIELD_N] <> ''
for xml path ('')
),1,1, '')
from [TABLE] t2