All bin_packing predicates crash when no items are given

[informarte]

All bin-packing predicates crash when no items are given. For example,

include "bin_packing.mzn";

constraint bin_packing(10, [], []);

results in

/tmp/bin_packing_test.mzn:3.12-34
  in call 'bin_packing'
/home/informarte/Software/lib/MiniZincIDE-2.8.7-bundle-linux-x86_64/share/minizinc/std/bin_packing.mzn:18.5-24.7
  in call 'assert'
/home/informarte/Software/lib/MiniZincIDE-2.8.7-bundle-linux-x86_64/share/minizinc/std/bin_packing.mzn:20.5-24.6
  in call 'assert'
  in binary '>=' operator expression
  in call 'lb_array'

I would expect the predicates to behave as follows when there are no items:

• bin_packing and bin_packing_capa reduce to true
• bin_packing_load(load, bin, w) reduces to forall(l in load)(l = 0)
• bin_packing_load_fn yields an empty array

Interestingly, cumulative does not suffer from this issue: When there are no tasks, it reduces to true.

[Dekker1]

Thank you for bringing this to our attention. Not too long ago, I went over a decent chunk of the global constraints to make sure that they work with “empty” input, but I must have missed these.