Change null check to empty lists

broker/src/main/java/org/eclipse/moquette/spi/impl/MemoryStorageService.java

@@ -28,6 +28,8 @@ import org.eclipse.moquette.spi.ISessionsStore;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import static org.eclipse.moquette.spi.impl.Utils.defaultGet;
+
 /**
  */
 public class MemoryStorageService implements IMessagesStore, ISessionsStore {
@@ -81,20 +83,21 @@ public class MemoryStorageService implements IMessagesStore, ISessionsStore {
     @Override
     public void storePublishForFuture(PublishEvent evt) {
         LOG.debug("storePublishForFuture store evt {}", evt);
-        List<PublishEvent> storedEvents;
+//        List<PublishEvent> storedEvents;
         String clientID = evt.getClientID();
-        if (!m_persistentMessageStore.containsKey(clientID)) {
-            storedEvents = new ArrayList<PublishEvent>();
-        } else {
-            storedEvents = m_persistentMessageStore.get(clientID);
-        }
+//        if (!m_persistentMessageStore.containsKey(clientID)) {
+//            storedEvents = new ArrayList<PublishEvent>();
+//        } else {
+//            storedEvents = m_persistentMessageStore.get(clientID);
+//        }
+        List<PublishEvent> storedEvents = defaultGet(m_persistentMessageStore, clientID, new ArrayList<PublishEvent>());
         storedEvents.add(evt);
         m_persistentMessageStore.put(clientID, storedEvents);
     }
 
     @Override
     public List<PublishEvent> listMessagesInSession(String clientID) {
-        return new ArrayList<>(m_persistentMessageStore.get(clientID));
+        return new ArrayList<>(defaultGet(m_persistentMessageStore, clientID, Collections.<PublishEvent>emptyList()));
     }
     
     @Override

broker/src/main/java/org/eclipse/moquette/spi/impl/ProtocolProcessor.java

@@ -242,7 +242,7 @@ class ProtocolProcessor implements EventHandler<ValueEvent> {
     private void republishStoredInSession(String clientID) {
         LOG.trace("republishStoredInSession invoked");
         List<PublishEvent> publishedEvents = m_messagesStore.listMessagesInSession(clientID);
-        if (publishedEvents == null) {
+        if (publishedEvents.isEmpty()) {
             LOG.info("No stored messages for client <{}>", clientID);
             return;
         }

broker/src/main/java/org/eclipse/moquette/spi/impl/Utils.java

@@ -0,0 +1,16 @@
+package org.eclipse.moquette.spi.impl;
+
+import java.util.Map;
+
+/**
+ * Utility static methods, like Map get with default value, or elvis operator.
+ */
+public class Utils {
+    public static <T, K> T defaultGet(Map<K, T> map, K key, T defaultValue) {
+        T value = map.get(key);
+        if (value != null) {
+            return value;
+        }
+        return defaultValue;
+    }
+}

broker/src/main/java/org/eclipse/moquette/spi/persistence/MapDBPersistentStore.java

@@ -25,6 +25,8 @@ import org.eclipse.moquette.spi.impl.storage.StoredPublishEvent;
 import org.eclipse.moquette.spi.impl.subscriptions.Subscription;
 import org.eclipse.moquette.proto.messages.AbstractMessage;
 import static org.eclipse.moquette.server.Server.STORAGE_FILE_PATH;
+import static org.eclipse.moquette.spi.impl.Utils.defaultGet;
+
 import org.mapdb.DB;
 import org.mapdb.DBMaker;
 import org.slf4j.Logger;
@@ -126,11 +128,9 @@ public class MapDBPersistentStore implements IMessagesStore, ISessionsStore {
 
     @Override
     public List<PublishEvent> listMessagesInSession(String clientID) {
-        List<StoredPublishEvent> storedEvts = m_persistentMessageStore.get(clientID);
-        if (storedEvts == null) {
-            return null;
-        }
-        List<PublishEvent> liveEvts = new ArrayList<PublishEvent>();
+        List<PublishEvent> liveEvts = new ArrayList<>();
+        List<StoredPublishEvent> storedEvts = defaultGet(m_persistentMessageStore, clientID, Collections.<StoredPublishEvent>emptyList());
+
         for (StoredPublishEvent storedEvt : storedEvts) {
             liveEvts.add(convertFromStored(storedEvt));
         }