fix: fix getu with parameter symbols

Author: AayushSabharwal

src/state_indexing.jl

@@ -95,7 +95,8 @@ function _getu(sys, ::ScalarSymbolic, ::SymbolicTypeTrait, sym)
         return getu(sys, idx)
     elseif is_parameter(sys, sym)
         return let fn = getp(sys, sym)
-            getter(prob, args...) = fn(prob)
+            getter(prob) = fn(prob)
+            getter(prob, i) = fn(parameter_values_at_state_time(prob, i))
             getter
         end
     elseif is_independent_variable(sys, sym)