Minor fixes. Update rule node UI

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

@@ -128,7 +128,7 @@ public class RuleNodeMvelScriptEngine extends RuleNodeScriptEngine<MvelInvokeSer
         } else {
             args[0] = new HashMap<>();
         }
-        args[1] = msg.getMetaData().getData();
+        args[1] = new HashMap<>(msg.getMetaData().getData());
         args[2] = msg.getType();
         return args;
     }

common/script/script-api/src/main/java/org/thingsboard/script/api/mvel/TbJson.java

@@ -0,0 +1,59 @@
+/**
+ * Copyright © 2016-2022 The Thingsboard Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.thingsboard.script.api.mvel;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import org.thingsboard.common.util.JacksonUtil;
+
+import java.io.IOException;
+import java.util.List;
+import java.util.Map;
+
+public class TbJson {
+
+    public static String stringify(Object value) {
+        return value != null ? JacksonUtil.toString(value) : "null";
+    }
+
+    public static Object parse(String value) throws IOException {
+        if (value != null) {
+            JsonNode node = JacksonUtil.toJsonNode(value);
+            if (node.isObject()) {
+                return JacksonUtil.convertValue(node, Map.class);
+            } else if (node.isArray()) {
+                return JacksonUtil.convertValue(node, List.class);
+            } else if (node.isDouble()) {
+                return node.doubleValue();
+            } else if (node.isLong()) {
+                return node.longValue();
+            } else if (node.isInt()) {
+                return node.intValue();
+            } else if (node.isBoolean()) {
+                return node.booleanValue();
+            } else if (node.isTextual()) {
+                return node.asText();
+            } else if (node.isBinary()) {
+                return node.binaryValue();
+            } else if (node.isNull()) {
+                return null;
+            } else {
+                return node.asText();
+            }
+        } else {
+            return null;
+        }
+    }
+}

common/script/script-api/src/main/java/org/thingsboard/script/api/mvel/TbMvelClassLoader.java

@@ -46,6 +46,8 @@ public class TbMvelClassLoader extends URLClassLoader {
         AbstractParser.CLASS_LITERALS.remove("Compiler");
         AbstractParser.CLASS_LITERALS.remove("ThreadLocal");
         AbstractParser.CLASS_LITERALS.remove("SecurityManager");
+        AbstractParser.CLASS_LITERALS.put("JSON", TbJson.class);
+        AbstractParser.LITERALS.put("JSON", TbJson.class);
 
         AbstractParser.CLASS_LITERALS.values().forEach(val -> allowedClasses.add(((Class) val).getName()));
     }

rule-engine/rule-engine-components/src/main/java/org/thingsboard/rule/engine/action/TbAbstractAlarmNodeConfiguration.java

@@ -35,10 +35,10 @@ public abstract class TbAbstractAlarmNodeConfiguration {
 
     static final String ALARM_DETAILS_BUILD_MVEL_TEMPLATE = "" +
             "var details = {};\n" +
-            "if (metadata.prevAlarmDetails) {\n" +
+            "if (metadata.prevAlarmDetails != null) {\n" +
             "    details = JSON.parse(metadata.prevAlarmDetails);\n" +
             "    //remove prevAlarmDetails from metadata\n" +
-            "    delete metadata.prevAlarmDetails;\n" +
+            "    metadata.remove('prevAlarmDetails');\n" +
             "    //now metadata is the same as it comes IN this rule node\n" +
             "}\n" +
             "\n" +