Show an avatar, description or away message being cleared

Client and channel updates were only applied when the field had a
value, since ts3j reads a missing field back as an empty string. A
removed avatar, an emptied description or a cleared away message
arrives as the field without a value, so they stayed as they were. Such
fields are now applied whenever the update carries them.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

ts3-client/core/src/test/java/com/ts3client/net/EventFieldsTest.java

@@ -1,12 +1,16 @@
 package com.ts3client.net;
 
+import com.github.manevolent.ts3j.command.MultiCommand;
 import com.github.manevolent.ts3j.event.ClientUpdatedEvent;
+import com.github.manevolent.ts3j.protocol.ProtocolRole;
 import org.junit.jupiter.api.Test;
 
 import java.util.Map;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 /**
  * Pins the ts3j behaviour {@code ConnectionEventHandler.has(...)} exists for: a field
@@ -22,4 +26,15 @@ class EventFieldsTest {
         assertEquals("", e.get("client_is_recording"));
         assertEquals("", e.get("client_nickname"));
     }
+
+    /** What {@code reported(...)} relies on: a cleared field still arrives, just without a value. */
+    @Test
+    void clearedFieldsAreStillInTheMap() {
+        Map<String, String> fields = MultiCommand.parse(ProtocolRole.SERVER,
+                "notifyclientupdated clid=7 client_flag_avatar client_description=").simplifyOne().toMap();
+        ClientUpdatedEvent e = new ClientUpdatedEvent(fields);
+        assertTrue(e.getMap().containsKey("client_flag_avatar"));
+        assertTrue(e.getMap().containsKey("client_description"));
+        assertFalse(e.getMap().containsKey("client_away_message"));
+    }
 }