fix: eth: ensure that the event topics are non-nil

Even when empty.

fixes #10910

node/impl/full/eth.go

@@ -1537,6 +1537,8 @@ func ethLogFromEvent(entries []types.EventEntry) (data []byte, topics []ethtypes
 		topicsFoundCount int
 		dataFound        bool
 	)
+	// Topics must be non-nil, even if empty. So we might as well pre-allocate for 4 (the max).
+	topics = make([]ethtypes.EthHash, 0, 4)
 	for _, entry := range entries {
 		// Drop events with non-raw topics to avoid mistakes.
 		if entry.Codec != cid.Raw {

node/impl/full/eth_test.go

@@ -17,7 +17,8 @@ func TestEthLogFromEvent(t *testing.T) {
 	data, topics, ok := ethLogFromEvent(nil)
 	require.True(t, ok)
 	require.Nil(t, data)
-	require.Nil(t, topics)
+	require.Empty(t, topics)
+	require.NotNil(t, topics)
 
 	// basic topic
 	data, topics, ok = ethLogFromEvent([]types.EventEntry{{