unnecessary cast will be added on children in CaseExpr because use symbolized equal to compare to `Expr`'s type. it will lead to expression compare mistake and then lead to expression substitute failed when use `ExprSubstitutionMap`
unnecessary cast will be added on children in CaseExpr because use symbolized equal to compare to `Expr`'s type. it will lead to expression compare mistake and then lead to expression substitute failed when use `ExprSubstitutionMap`