Fix NPE in rule node mvel script engine while metadata unbinding. Update MVEL dependency version

application/src/main/java/org/thingsboard/server/service/script/RuleNodeMvelScriptEngine.java

@@ -143,7 +143,8 @@ public class RuleNodeMvelScriptEngine extends RuleNodeScriptEngine<MvelInvokeSer
         if (msgData.containsKey(RuleNodeScriptFactory.METADATA)) {
             Object msgMetadataObj = msgData.get(RuleNodeScriptFactory.METADATA);
             if (msgMetadataObj instanceof Map) {
-                metadata = ((Map<?, ?>) msgMetadataObj).entrySet().stream().collect(Collectors.toMap(e -> e.getKey().toString(), e -> e.getValue().toString()));
+                metadata = ((Map<?, ?>) msgMetadataObj).entrySet().stream().filter(e -> e.getValue() != null)
+                        .collect(Collectors.toMap(e -> e.getKey().toString(), e -> e.getValue().toString()));
             } else {
                 metadata = JacksonUtil.convertValue(msgMetadataObj, new TypeReference<>() {
                 });

pom.xml

@@ -77,7 +77,7 @@
         <zookeeper.version>3.5.5</zookeeper.version>
         <protobuf.version>3.17.2</protobuf.version>
         <grpc.version>1.42.1</grpc.version>
-        <mvel.version>2.4.20TB</mvel.version>
+        <mvel.version>2.4.21TB</mvel.version>
         <lombok.version>1.18.18</lombok.version>
         <paho.client.version>1.2.4</paho.client.version>
         <netty.version>4.1.75.Final</netty.version>