Block: Avoid NPE in hasTransactions()
Field is nullable;
```java
List<Transaction> transactions;
```
@@ -1003,7 +1003,7 @@ public class Block extends Message {
* purely a header).
*/
public boolean hasTransactions() {
- return !this.transactions.isEmpty();
+ return (this.transactions != null) && !this.transactions.isEmpty();
}
/**
