You need to add a post processing step to fill in the missing values with the previous value:
{
for (let m of icu.fit) {
if (m._num !== 104) continue
let ts = m.f_253.value
if (ts) data.setAt(ts, m.f_2.value)
}
let prev
for (let i = 0; i < data.length; i++) {
if (data[i]) prev = data[i]
else data[i] = prev
}
}