Fix an NPE when validating an examples trait

smithy-model/src/main/java/software/amazon/smithy/model/traits/ExamplesTrait.java

@@ -167,8 +167,8 @@ public static Builder builder() {
         public static final class Builder implements SmithyBuilder<Example> {
             private String title;
             private String documentation;
-            private ObjectNode input;
-            private ObjectNode output;
+            private ObjectNode input = Node.objectNode();
+            private ObjectNode output = Node.objectNode();
 
             @Override
             public Example build() {

smithy-model/src/test/java/software/amazon/smithy/model/validation/ExamplesTraitValidatorTest.java

@@ -0,0 +1,32 @@
+package software.amazon.smithy.model.validation;
+
+import org.junit.jupiter.api.Test;
+import software.amazon.smithy.model.Model;
+import software.amazon.smithy.model.shapes.OperationShape;
+import software.amazon.smithy.model.shapes.Shape;
+import software.amazon.smithy.model.traits.ExamplesTrait;
+import software.amazon.smithy.model.validation.validators.ExamplesTraitValidator;
+
+public class ExamplesTraitValidatorTest {
+    // There was an NPE previously due to the input/output values
+    // in the builder for an ExamplesTrait.Example not being
+    // initialized to an empty ObjectNode.
+    @Test
+    public void noNpeWhenInputOrOutputAreOmitted() {
+        ExamplesTrait.Example example = ExamplesTrait.Example.builder()
+                .title("Title")
+                .documentation("Documentation")
+                .build();
+        ExamplesTrait trait = ExamplesTrait.builder().addExample(example).build();
+        Shape shape = OperationShape.builder()
+                .id("foo.bar#Baz")
+                .addTrait(trait)
+                .build();
+        Model model = Model.builder().addShape(shape).build();
+
+        ExamplesTraitValidator validator = new ExamplesTraitValidator();
+
+        // Just make sure it doesn't throw.
+        validator.validate(model);
+    }
+}