fix: fix remake_initializeprob handling of no pre-existing initializeprob

Author: AayushSabharwal

src/systems/nonlinear/initializesystem.jl

@@ -291,33 +291,10 @@ function SciMLBase.remake_initialization_data(sys::ODESystem, odefn, u0, t0, p,
         end
     else
         # there is no initializeprob, so the original problem construction
-        # had no solvable parameters and had the differential variables
-        # specified in `u0map`.
-        if u0 === missing
-            # the user didn't pass `u0` to `remake`, so they want to retain
-            # existing values. Fill the differential variables in `u0map`,
-            # initialization will either be elided or solve for the algebraic
-            # variables
-            diff_idxs = isdiffeq.(equations(sys))
-            for i in eachindex(dvs)
-                diff_idxs[i] || continue
-                u0map[dvs[i]] = newu0[i]
-            end
-        end
-        if p === missing
-            # the user didn't pass `p` to `remake`, so they want to retain
-            # existing values. Fill all parameters in `pmap` so that none of
-            # them are solvable.
-            for p in ps
-                pmap[p] = getp(sys, p)(newp)
-            end
-        end
-        # all non-solvable parameters need values regardless
-        for p in ps
-            haskey(pmap, p) && continue
-            is_parameter_solvable(p, pmap, defs, guesses) && continue
-            pmap[p] = getp(sys, p)(newp)
-        end
+        # had all variables specified in `u0map`, all parameters specified
+        # and no parameter dependencies specified.
+        add_fallbacks!(u0map, dvs, to_varmap(Dict(dvs .=> newu0), dvs))
+        add_fallbacks!(pmap, ps, to_varmap(Dict(k => getp(sys, k)(newp) for k in ps), ps))
     end
     if t0 === nothing
         t0 = 0.0