add check for empty lists in txpool (ethereum#704)

* add check

* linters

Author: JekaMas

core/tx_list.go

@@ -351,9 +351,8 @@ func (m *txSortedMap) lastElement() *types.Transaction {
 
 		m.cacheMu.Unlock()
 
-		cache = make(types.Transactions, 0, len(m.items))
-
 		m.m.RLock()
+		cache = make(types.Transactions, 0, len(m.items))
 
 		for _, tx := range m.items {
 			cache = append(cache, tx)
@@ -373,6 +372,11 @@ func (m *txSortedMap) lastElement() *types.Transaction {
 		hitCacheCounter.Inc(1)
 	}
 
+	ln := len(cache)
+	if ln == 0 {
+		return nil
+	}
+
 	return cache[len(cache)-1]
 }
 

core/tx_pool.go

@@ -1539,6 +1539,7 @@ func (pool *TxPool) runReorg(ctx context.Context, done chan struct{}, reset *txp
 		// remove any transaction that has been included in the block or was invalidated
 		// because of another transaction (e.g. higher gas price).
 
+		//nolint:nestif
 		if reset != nil {
 			tracing.ElapsedTime(ctx, span, "new block", func(_ context.Context, innerSpan trace.Span) {
 
@@ -1573,7 +1574,9 @@ func (pool *TxPool) runReorg(ctx context.Context, done chan struct{}, reset *txp
 				tracing.ElapsedTime(ctx, innerSpan, "09 fill nonces", func(_ context.Context, innerSpan trace.Span) {
 					for addr, list := range pool.pending {
 						highestPending = list.LastElement()
-						nonces[addr] = highestPending.Nonce() + 1
+						if highestPending != nil {
+							nonces[addr] = highestPending.Nonce() + 1
+						}
 					}
 				})