Fix namespace_guesses

Author: YingboMa

src/systems/abstractsystem.jl

@@ -867,7 +867,10 @@ end
 
 function namespace_guesses(sys)
     guess = guesses(sys)
-    Dict(unknowns(sys, k) => namespace_expr(v, sys) for (k, v) in guess)
+    Dict((vv = unwrap(v);
+         kk = unwrap(k);
+         unknowns(sys, kk) => vv isa Symbolic ? namespace_expr(v, sys) : vv)
+    for (k, v) in guess)
 end
 
 function namespace_equations(sys::AbstractSystem, ivs = independent_variables(sys))