fix: fix and test getu and getp with empty arrays

src/parameter_indexing.jl

@@ -323,6 +323,10 @@ struct MultipleParametersGetter{T <: IsIndexerTimeseries, G, I} <:
 end
 
 function MultipleParametersGetter(getters)
+    if isempty(getters)
+        return MultipleParametersGetter{IndexerNotTimeseries, typeof(getters), Nothing}(
+            getters, nothing)
+    end
     has_timeseries_indexers = any(getters) do g
         is_indexer_timeseries(g) == IndexerTimeseries()
     end

src/state_indexing.jl

@@ -236,7 +236,7 @@ for (t1, t2) in [
     @eval function _getu(sys, ::NotSymbolic, ::$t1, sym::$t2)
         num_observed = count(x -> is_observed(sys, x), sym)
         if num_observed == 0 || num_observed == 1 && sym isa Tuple
-            if all(Base.Fix1(is_parameter, sys), sym) &&
+            if !isempty(sym) && all(Base.Fix1(is_parameter, sys), sym) &&
                all(!Base.Fix1(is_timeseries_parameter, sys), sym)
                 GetpAtStateTime(getp(sys, sym))
             else

test/parameter_indexing_test.jl

@@ -123,9 +123,23 @@ for sys in [
                 @test buffer == collect(val)
             end
         end
+
+        getter = getp(sys, [])
+        @test getter(fi) == []
+        getter = getp(sys, ())
+        @test getter(fi) == ()
     end
 end
 
+let
+    sc = SymbolCache(nothing, nothing, :t)
+    fi = FakeIntegrator(sc, nothing, 0.0, Ref(0))
+    getter = getp(sc, [])
+    @test getter(fi) == []
+    getter = getp(sc, ())
+    @test getter(fi) == ()
+end
+
 struct MyDiffEqArray
     t::Vector{Float64}
     u::Vector{Vector{Float64}}
@@ -387,6 +401,13 @@ end
 
 @test_throws ErrorException getp(sys, :not_a_param)
 
+let fs = fs, sys = sys
+    getter = getp(sys, [])
+    @test getter(fs) == []
+    getter = getp(sys, ())
+    @test getter(fs) == ()
+end
+
 struct FakeNoTimeSolution
     sys::SymbolCache
     u::Vector{Float64}

test/state_indexing_test.jl

@@ -91,6 +91,19 @@ for (sym, val, check_inference) in [
     @test get(fi) == val
 end
 
+let fi = fi, sys = sys
+    getter = getu(sys, [])
+    @test getter(fi) == []
+    getter = getu(sys, ())
+    @test getter(fi) == ()
+    sc = SymbolCache(nothing, [:a, :b], :t)
+    fi = FakeIntegrator(sys, nothing, [1.0, 2.0], 3.0)
+    getter = getu(sc, [])
+    @test getter(fi) == []
+    getter = getu(sc, ())
+    @test getter(fi) == ()
+end
+
 for (sym, oldval, newval, check_inference) in [(:a, p[1], 4.0, true)
                                                (:b, p[2], 5.0, true)
                                                (:c, p[3], 6.0, true)
@@ -232,6 +245,19 @@ for (sym, val) in [(:a, p[1])
     @test get(sol) == val
 end
 
+let sol = sol, sys = sys
+    getter = getu(sys, [])
+    @test getter(sol) == [[] for _ in 1:length(sol.t)]
+    getter = getu(sys, ())
+    @test getter(sol) == [() for _ in 1:length(sol.t)]
+    sc = SymbolCache(nothing, [:a, :b], :t)
+    sol = FakeSolution(sys, [], [1.0, 2.0], [])
+    getter = getu(sc, [])
+    @test getter(sol) == []
+    getter = getu(sc, ())
+    @test getter(sol) == []
+end
+
 sys = SymbolCache([:x, :y, :z], [:a, :b, :c])
 u = [1.0, 2.0, 3.0]
 p = [10.0, 20.0, 30.0]