chore: handle nothing dtunables for SteadyStateAdjoint

Author: DhairyaLGandhi

Project.toml

@@ -1,7 +1,7 @@
 name = "SciMLSensitivity"
 uuid = "1ed8b502-d754-442c-8d5d-10ac956f44a1"
 authors = ["Christopher Rackauckas <[email protected]>", "Yingbo Ma <[email protected]>"]
-version = "7.76.0"
+version = "7.77.0"
 
 [deps]
 ADTypes = "47edcb42-4c32-4615-8424-f2b9edc5f35b"

src/concrete_solve.jl

@@ -1793,7 +1793,7 @@ function DiffEqBase._concrete_solve_adjoint(
             end
         end
 
-        dp = Zygote.accum(dp, isempty(Δtunables) ? nothing : Δtunables)
+        dp = Zygote.accum(dp, (isempty(Δtunables) || isnothing(Δtunables)) ? nothing : Δtunables)
 
         if originator isa SciMLBase.TrackerOriginator ||
            originator isa SciMLBase.ReverseDiffOriginator