MicroProfile GraphQL: Minor update to README and add missing @NonNull on TaskApi

examples/microprofile/graphql/README.md

@@ -35,18 +35,18 @@ Access the `/graphql` endpoint via `http://127.0.0.1:7001/graphql`:
     ```graphql
     type Mutation {
       "Create a task with the given description"
-      createTask(description: String): Task
+      createTask(description: String!): Task
       "Remove all completed tasks and return the tasks left"
       deleteCompletedTasks: [Task]
       "Delete a task and return the deleted task details"
-      deleteTask(id: String): Task
+      deleteTask(id: String!): Task
       "Update a task"
-      updateTask(completed: Boolean, description: String, id: String): Task
+      updateTask(completed: Boolean, description: String, id: String!): Task
     }
 
     type Query {
       "Return a given task"
-      findTask(id: String): Task
+      findTask(id: String!): Task
       "Query tasks and optionally specified only completed"
       tasks(completed: Boolean): [Task]
     }

examples/microprofile/graphql/src/main/java/io/helidon/examples/graphql/basics/TaskApi.java

@@ -51,7 +51,7 @@ public class TaskApi {
      */
     @Mutation
     @Description("Create a task with the given description")
-    public Task createTask(@Name("description") String description) {
+    public Task createTask(@Name("description") @NonNull String description) {
         if (description == null) {
             throw new IllegalArgumentException("Description must be provided");
         }