Set τrec if it is not nothing

Author: hersle

src/solve.jl

@@ -332,10 +332,12 @@ function solvebg(bgprob::ODEProblem; alg = DEFAULT_BGALG, reltol = 1e-9, abstol
     if !successful_retcode(bgsol)
         @warn warning_failed_solution(bgsol, "Background"; verbose)
     end
-    if Symbol("τrec") in Symbol.(parameters(bgprob.f.sys))
-        τrecidx = ModelingToolkit.parameter_index(bgprob, :τrec)
+
+    τrecidx = ModelingToolkit.parameter_index(bgprob, :τrec)
+    if !isnothing(τrecidx)
         bgsol.ps[τrecidx] = bgsol[:τ][argmax(bgsol[bgprob.f.sys.b.v])]
     end
+
     return bgsol
 end
 # TODO: more generic shooting method that can do anything (e.g. S8)