Improve error handling of empty iterators

Author: Jack Dunham

src/iterators.jl

@@ -47,8 +47,13 @@ mutable struct RegionIterator{Problem, RegionPlan} <: AbstractNetworkIterator
     which_region::Int
     const which_sweep::Int
     function RegionIterator(problem::P, region_plan::R, sweep::Int) where {P, R}
-        if length(region_plan) == 0
-            throw(BoundsError("Cannot construct a region iterator with 0 elements."))
+        try
+            first(region_plan)
+        catch e
+            if e isa BoundsError
+                throw(ArgumentError("Cannot construct a region iterator with 0 elements."))
+            end
+            rethrow()
         end
         return new{P, R}(problem, region_plan, 1, sweep)
     end
@@ -125,10 +130,11 @@ mutable struct SweepIterator{Problem, Iter} <: AbstractNetworkIterator
     which_sweep::Int
     function SweepIterator(problem::Prob, sweep_kwargs::Iter) where {Prob, Iter}
         stateful_sweep_kwargs = Iterators.Stateful(sweep_kwargs)
+
         first_state = Iterators.peel(stateful_sweep_kwargs)
 
         if isnothing(first_state)
-            throw(BoundsError("Cannot construct a sweep iterator with 0 elements."))
+            throw(ArgumentError("Cannot construct a sweep iterator with 0 elements."))
         end
 
         first_kwargs, _ = first_state

test/test_iterators.jl

@@ -65,8 +65,8 @@ end
             @test only(cb) == 1
 
             prob = TestIteratorUtils.TestProblem([])
-            @test_throws BoundsError SweepIterator(prob, 0)
-            @test_throws BoundsError RegionIterator(prob, [], 1)
+            @test_throws ArgumentError SweepIterator(prob, 0)
+            @test_throws ArgumentError RegionIterator(prob, [], 1)
         end
 
         TI = TestIteratorUtils.TestIterator(1, 4, [])