Default Math Node configuration fix

rule-engine/rule-engine-components/src/main/java/org/thingsboard/rule/engine/math/TbMathArgument.java

@@ -34,4 +34,8 @@ public class TbMathArgument {
        this(key, type, key, null, null);
     }
 
+    public TbMathArgument(String name, TbMathArgumentType type, String key) {
+       this(name, type, key, null, null);
+    }
+
 }

rule-engine/rule-engine-components/src/main/java/org/thingsboard/rule/engine/math/TbMathNodeConfiguration.java

@@ -33,7 +33,7 @@ public class TbMathNodeConfiguration implements NodeConfiguration<TbMathNodeConf
     public TbMathNodeConfiguration defaultConfiguration() {
         TbMathNodeConfiguration configuration = new TbMathNodeConfiguration();
         configuration.setOperation(TbRuleNodeMathFunctionType.ADD);
-        configuration.setArguments(Arrays.asList(new TbMathArgument(TbMathArgumentType.CONSTANT, "2"), new TbMathArgument(TbMathArgumentType.CONSTANT, "2")));
+        configuration.setArguments(Arrays.asList(new TbMathArgument("x", TbMathArgumentType.CONSTANT, "2"), new TbMathArgument("y", TbMathArgumentType.CONSTANT, "2")));
         configuration.setResult(new TbMathResult(TbMathArgumentType.MESSAGE_BODY, "result", 2, false, false, null));
         return configuration;
     }