Internal function: return character(0) instead of NULL.
This is sometimes needed not to return error when applying some functions.
Usage
nn(x)
Value
character(0) if x==NULL, x elsewhere
Arguments
x
Input variable
Author
Luigi Ranghetti, phD (2019)
References
L. Ranghetti, M. Boschetti, F. Nutini, L. Busetto (2020).
"sen2r": An R toolbox for automatically downloading and preprocessing
Sentinel-2 satellite data. Computers & Geosciences, 139, 104473.
tools:::Rd_expr_doi("10.1016/j.cageo.2020.104473"), URL: https://sen2r.ranghetti.info/.