Merge branch '4.1'

Conflicts:
	smack-extensions/src/main/java/org/jivesoftware/smackx/bytestreams/socks5/Socks5BytestreamManager.java
	version.gradle

smack-core/src/main/java/org/jivesoftware/smack/packet/Presence.java

@@ -19,6 +19,7 @@ package org.jivesoftware.smack.packet;
 
 import java.util.Locale;
 
+import org.jivesoftware.smack.packet.id.StanzaIdUtil;
 import org.jivesoftware.smack.util.Objects;
 import org.jivesoftware.smack.util.TypedCloneable;
 import org.jivesoftware.smack.util.XmlStringBuilder;
@@ -259,6 +260,18 @@ public final class Presence extends Stanza implements TypedCloneable<Presence> {
         return new Presence(this);
     }
 
+    /**
+     * Clone this presence and set a newly generated stanza ID as the clone's ID.
+     *
+     * @return a "clone" of this presence  with a different stanza ID.
+     * @since 4.1.2
+     */
+    public Presence cloneWithNewId() {
+        Presence clone = clone();
+        clone.setStanzaId(StanzaIdUtil.newStanzaId());
+        return clone;
+    }
+
     /**
      * An enum to represent the presence type. Note that presence type is often confused
      * with presence mode. Generally, if a user is signed in to a server, they have a presence

smack-core/src/main/java/org/jivesoftware/smack/packet/Stanza.java

@@ -359,6 +359,23 @@ public abstract class Stanza implements TopLevelStreamElement {
         }
     }
 
+    /**
+     * Add the given extension and override eventually existing extensions with the same name and
+     * namespace.
+     *
+     * @param extension the extension element to add.
+     * @return one of the removed extensions or <code>null</code> if there are none.
+     * @since 4.1.2
+     */
+    public ExtensionElement overrideExtension(ExtensionElement extension) {
+        if (extension == null) return null;
+        synchronized (packetExtensions) {
+            ExtensionElement removedExtension = removeExtension(extension);
+            addExtension(extension);
+            return removedExtension;
+        }
+    }
+
     /**
      * Adds a collection of stanza(/packet) extensions to the packet. Does nothing if extensions is null.
      * 

smack-core/src/main/java/org/jivesoftware/smack/sasl/SASLMechanism.java

@@ -201,7 +201,10 @@ public abstract class SASLMechanism implements Comparable<SASLMechanism> {
     private final void authenticate() throws SmackException, NotConnectedException, InterruptedException {
         byte[] authenticationBytes = getAuthenticationText();
         String authenticationText;
-        if (authenticationBytes != null) {
+        // Some SASL mechanisms do return an empty array (e.g. EXTERNAL from javax), so check that
+        // the array is not-empty. Mechanisms are allowed to return either 'null' or an empty array
+        // if there is no authentication text.
+        if (authenticationBytes != null && authenticationBytes.length > 0) {
             authenticationText = Base64.encodeToString(authenticationBytes);
         } else {
             // RFC6120 6.4.2 "If the initiating entity needs to send a zero-length initial response,
@@ -215,7 +218,8 @@ public abstract class SASLMechanism implements Comparable<SASLMechanism> {
 
     /**
      * Should return the initial response of the SASL mechanism. The returned byte array will be
-     * send base64 encoded to the server. SASL mechanism are free to return <code>null</code> here.
+     * send base64 encoded to the server. SASL mechanism are free to return <code>null</code> or an
+     * empty array here.
      * 
      * @return the initial response or null
      * @throws SmackException