Handle empty Kwargs case in forwarddiff detection

Fixes #1074

Author: ChrisRackauckas

src/forwarddiff.jl

@@ -363,11 +363,14 @@ function anyeltypedual(x::NamedTuple, ::Type{Val{counter}} = Val{0}) where {coun
     anyeltypedual(values(x))
 end
 
-function DiffEqBase.anyeltypedual(
+function anyeltypedual(
         f::SciMLBase.AbstractSciMLFunction, ::Type{Val{counter}}) where {counter}
     Any
 end
 
+anyeltypedual(::@Kwargs{}, ::Type{Val{counter}} = Val{0}) where {counter} = Any
+anyeltypedual(::Type{@Kwargs{}}, ::Type{Val{counter}} = Val{0}) where {counter} = Any
+
 @inline promote_u0(::Nothing, p, t0) = nothing
 
 @inline function promote_u0(u0, p, t0)

test/forwarddiff_dual_detection.jl

@@ -36,7 +36,7 @@ p_possibilities = [ForwardDiff.Dual(2.0), (ForwardDiff.Dual(2.0), 2.0),
     (; x = 2.0, y = [ForwardDiff.Dual(2.0)]), (; x = 2.0, y = [[ForwardDiff.Dual(2.0)]]),
     Set([2.0, ForwardDiff.Dual(2.0)]), (SciMLBase.NullParameters(), ForwardDiff.Dual(2.0)),
     ((), ForwardDiff.Dual(2.0)), ForwardDiff.Dual{Nothing}(ForwardDiff.Dual{MyStruct}(2.0)),
-    (plot(), ForwardDiff.Dual(2.0)), [(1.0, ForwardDiff.Dual(1.0, (1.0,)))]
+    (plot(), ForwardDiff.Dual(2.0)), [(1.0, ForwardDiff.Dual(1.0, (1.0,))), pairs((;))]
 ]
 
 for p in p_possibilities