This only occurs during compilation if the compiler recognizes a statement that is trying to move an illegal value into a numeric field as this is not allowed.
So if you have something like:
01 my-group.
05 num-field pic 9(5).
01 aspace pic x value space.
and you try:
move space to num-field *> you will get zero substitution because compiler knows illegal value
but if you use instead the data-item aspace
move aspace to num-field *> no compiler error but you may get rts163 error at run-time. if test for 0 fails
if you move spaces to the group item you will not get compiler error but may get rts163 error at run-time but if test for 0 fails
move space to my-group
if num-field = 0
display "yes"
else
display "no"
end-if