refactor: add error message for wrapped variable in collect_var!

Author: AayushSabharwal

src/utils.jl

@@ -606,6 +606,17 @@ end
 
 function collect_var!(unknowns, parameters, var, iv; depth = 0)
     isequal(var, iv) && return nothing
+    if Symbolics.iswrapped(var)
+        error("""
+        Internal Error. Please open an issue with an MWE.
+
+        Encountered a wrapped value in `collect_var!`. This function should only ever \
+        receive unwrapped symbolic variables. This is likely a bug in the code generating \
+        an expression passed to `collect_vars!` or `collect_scoped_vars!`. A common cause \
+        is using `substitute` or `fast_substitute` with rules where the values are \
+        wrapped symbolic variables.
+        """)
+    end
     check_scope_depth(getmetadata(var, SymScope, LocalScope()), depth) || return nothing
     var = setmetadata(var, SymScope, LocalScope())
     if iscalledparameter(var)