Actually that created an ugly cycle: the constructor of the sentinel TypeVar tries to assign the sentinel to `_suspended`.

```
	at scala.reflect.internal.Types$TypeVar$.sentinelTypeVar(Types.scala:2851)
	at scala.reflect.internal.Types$TypeVar$.<init>(Types.scala:2852)
	at scala.reflect.internal.SymbolTable.TypeVar$lzycompute(SymbolTable.scala:14)
	at scala.reflect.internal.SymbolTable.TypeVar(SymbolTable.scala:14)
	at scala.reflect.internal.Types$TypeVar$.sentinelTypeVar(Types.scala:2851)
	at scala.reflect.internal.Types$TypeVar$.<init>(Types.scala:2852)
	at scala.reflect.internal.SymbolTable.TypeVar$lzycompute(SymbolTable.scala:14)
	at scala.reflect.internal.SymbolTable.TypeVar(SymbolTable.scala:14)
```

I'm inclined to leave it as is.