The litteral NULL cannot be used in a rule. In some cases it is useful to pass NULL explicitly to document default behaviour is desired.
e. g. :
validator( f( x=NULL ) == TRUE )
fails with:
'Error in if (length(x) == 1 || x[[1]] == "function") return x'
error happens as length(NULL) == 0.
The litteral
NULLcannot be used in a rule. In some cases it is useful to pass NULL explicitly to document default behaviour is desired.e. g. :
validator( f( x=NULL ) == TRUE )fails with:
'Error in if (length(x) == 1 || x[[1]] == "function") return x'
error happens as length(NULL) == 0.