Add the REST model to return an error or an message as a JSON.

src/main/java/space/kklochko/spring_rest_example/models/rest/RestError.java

@@ -0,0 +1,15 @@
+package space.kklochko.spring_rest_example.models.rest;
+
+import lombok.AllArgsConstructor;
+import lombok.Data;
+
+@AllArgsConstructor
+@Data
+public class RestError {
+    public String error;
+
+    public RestError() {
+        error = "";
+    }
+}
+

src/main/java/space/kklochko/spring_rest_example/models/rest/RestMessage.java

@@ -0,0 +1,15 @@
+package space.kklochko.spring_rest_example.models.rest;
+
+import lombok.AllArgsConstructor;
+import lombok.Data;
+
+@AllArgsConstructor
+@Data
+public class RestMessage {
+    public String message;
+
+    public RestMessage() {
+        message = "";
+    }
+}
+