fix: handle empty syms in concrete_getu

Author: AayushSabharwal

src/systems/problem_utils.jl

@@ -667,15 +667,19 @@ function get_mtkparameters_reconstructor(srcsys::AbstractSystem, dstsys::Abstrac
 
     # `syms[1]` is always the tunables because `srcsys` will have initials.
     tunable_syms = syms[1]
-    tunable_getter = p_constructor ∘ concrete_getu(srcsys, tunable_syms)
+    tunable_getter = if isempty(tunable_syms)
+        Returns(SizedVector{0, Float64})
+    else
+        p_constructor ∘ concrete_getu(srcsys, tunable_syms)
+    end
     rest_getters = map(Base.tail(Base.tail(syms))) do buf
         if buf == ()
             return Returns(())
         else
             return Base.Fix1(broadcast, p_constructor) ∘ getu(srcsys, buf)
         end
     end
-    initials_getter = if initials
+    initials_getter = if initials && !isempty(syms[2])
         initsyms = syms[2]
         allsyms = Set(all_symbols(srcsys))
         if unwrap_initials