Bug in import: Sometimes empty values are resolved as 0, which is wrong and causes problems

[Greenheart]

We should verify if values are numeric, and that the string representation of the cell value has some content.
Alternatively, check if the numeric value is 0, then the string value of the cell must also be explicitly "0", otherwise we should treat the value as undefined or null.

Instead of resolving this in the import script, we should probably double-check in the production DB (and potentially remove) all 0 values imported via the script. We could use the timestamp and the verifiiedBy, and potentially comment to find all occurences of this problem, and fix them manually via the API / editor.