nah, just default it to the powerset

Upon mature consideration, the powerset is the best default, if for no
other reason than it will force some people to consider the degenerate
case of 0 elements.

S32-setting-library/Containers.pod

@@ -577,7 +577,7 @@ C<.comb> on that string with the same parameters. See C<Str::comb>.
 =item combinations
 
  multi method combinations ( Int $of )
- multi method combinations ( Range $of = 1 .. * )
+ multi method combinations ( Range $of = 0 .. * )
 
 Returns all combinations of the list taken N at a time (specified
 by the C<$of> parameter).  If the range option is taken, returns all
@@ -591,6 +591,10 @@ container, so that subsets of sets can actually be a set of sets.
 If the ordering of the input doesn't matter, neither does the ordering
 of the subsets.)
 
+Note that, without an argument, the first returned combination will
+always be the empty list, and the last combination will always
+be the entire list.
+
 It is erroneous to ask for the combinations of any infinite list.
 The compiler is allowed to complain if it notices, however.
 
@@ -1119,14 +1123,13 @@ Works like an ordinary list C<roll>.
 =item combinations
 
  multi method combinations ( Int $of )
- multi method combinations ( Range $of = 1 .. * )
+ multi method combinations ( Range $of = 0 .. * )
 
 Works as if the set were turned into a list of elements and then
 the combinations were turned back into a list of sets, ordered by
 increasing size.  You may, of course, turn that list back into a set of sets.
 
-Note that, without an argument, this method does not quite calculate
-the powerset; you must explictly call with a range of 0..* for that.
+Note that, without an argument, this method basically calculates the powerset.
 
 =back