Fix optional arg unification for types with no optional args

trans/transpiler/phases/typing/types.py

@@ -203,7 +203,7 @@ class TypeOperator(BaseType, ABC):
                 continue
 
             if a is not None and b is None:
-                if i >= self.optional_at:
+                if self.optional_at is not None and i >= self.optional_at:
                     continue
                 else:
                     raise IncompatibleTypesError(f"Cannot unify {self} and {other}, not enough arguments")