fix(core/types): failing tests differentiating nil/empty optional slice

Author: ARR4N

core/types/block.libevm.go

@@ -134,7 +134,7 @@ func (b *Body) EncodeRLP(dst io.Writer) error {
 			return err
 		}
 
-		withdraws := len(b.Withdrawals) > 0
+		withdraws := b.Withdrawals != nil
 
 		// TODO(arr4n): call hook here, passing `withdraws` as a
 		// mustWriteEmptyOptional flag. The hook could also return a

rlp/list.libevm.go

@@ -47,7 +47,14 @@ func (s *Stream) FromList(fn func() error) error {
 }
 
 func DecodeList[T any](s *Stream) ([]*T, error) {
-	var vals []*T
+	// From the package-level documentation:
+	//
+	// > Note that package rlp never leaves a pointer-type struct field as nil
+	// > unless one of the "nil" struct tags is present.
+	//
+	// We therefore return a non-nil pointer to maintain said invariant as it
+	// makes use of this function easier.
+	vals := make([]*T, 0)
 	err := s.FromList(func() error {
 		for s.MoreDataInList() {
 			var v T