'data.frame': 31337 obs. of  16 variables:
  # $ ID                       : int  1 2 3 5 6 7 8 9 10 11 ...
  # $ Target                   : int  0 0 0 0 0 0 0 0 0 0 ...
  # $ band                     : chr  "3. 35 to 44" "NULL" "NULL" "NULL" ...
  # $ gender                   : chr  "Male" "NULL" "Male" "NULL" ...

is.null(NULL)
[1] TRUE
is.null("NULL")
[1] FALSE