galeShapley.collegeAdmissions() does not work properly when slots vector includes zero

[xerroxcopy]

I would like to set slots for some of the colleges zero, such as this:

studentPref <-
  matrix(data = c(1,2,3,4,1,2,3,4,1,2,3,4), nrow = 4)
collegePref <-
  matrix(data = c(1,2,3,1,2,3,1,2,3,1,2,3), nrow = 3)


galeShapley.collegeAdmissions(
  studentPref = studentPref,
  collegePref = collegePref,
  slots = c(1,2,0,0))

which returns

$matched.colleges
$matched.colleges[[1]]
[1] 1

$matched.colleges[[2]]
[1] 2 3

$matched.colleges[[3]]
[1] NA  3

$matched.colleges[[4]]
[1] NA  3


$matched.students
     [,1]
[1,]    1
[2,]    2
[3,]    4

I believe $matched.colleges[[3]], $matched.colleges[[4]] (both should be empty) as well as $matched.students[3,1] (should be 2) are wrong but I may be doing this wrong.
Setting slots = c(1,2,3,0) in the above example kind of works as expected, except for $matched.colleges[[4]] which should be empty instead of c(NA, NA).

Is it even possible to have zeros as elements of slots vector?