Create a dataset with implicit null for every selected columns
Arguments
- imp
 A list of implicit null data derived from get_implicit_col function
- year
 Selected year from the dataset
- colstr
 Column structure or Class type
- level
 Geographical granularity for aggregating data. See
getOption("orgdata.geo.levels")
See also
Other implicit-null functions:
do_implicit_null(),
find_implicit_col(),
get_implicit_col(),
get_implicit_per_year(),
get_implicit_ref()
