Minor refinements

Signed-off-by: fjtirado <[email protected]>

Author: fjtirado

impl/core/src/main/java/io/serverlessworkflow/impl/WorkflowApplication.java

@@ -103,26 +103,28 @@ public WorkflowIdFactory idFactory() {
   }
 
   public static class Builder {
-    private static final SchemaValidatorFactory EMPTY_SCHEMA_VALIDATOR =
-        new SchemaValidatorFactory() {
-
-          private final SchemaValidator NoValidation =
-              new SchemaValidator() {
-                @Override
-                public void validate(WorkflowModel node) {}
-              };
-
-          @Override
-          public SchemaValidator getValidator(StaticResource resource) {
-
-            return NoValidation;
-          }
-
-          @Override
-          public SchemaValidator getValidator(SchemaInline inline) {
-            return NoValidation;
-          }
-        };
+
+    private static final class EmptySchemaValidatorHolder {
+      private static final SchemaValidatorFactory instance =
+          new SchemaValidatorFactory() {
+            private final SchemaValidator NoValidation =
+                new SchemaValidator() {
+                  @Override
+                  public void validate(WorkflowModel node) {}
+                };
+
+            @Override
+            public SchemaValidator getValidator(StaticResource resource) {
+              return NoValidation;
+            }
+
+            @Override
+            public SchemaValidator getValidator(SchemaInline inline) {
+              return NoValidation;
+            }
+          };
+    }
+
     private TaskExecutorFactory taskFactory = DefaultTaskExecutorFactory.get();
     private ExpressionFactory exprFactory;
     private Collection<WorkflowExecutionListener> listeners;
@@ -207,7 +209,7 @@ public WorkflowApplication build() {
         schemaValidatorFactory =
             ServiceLoader.load(SchemaValidatorFactory.class)
                 .findFirst()
-                .orElse(EMPTY_SCHEMA_VALIDATOR);
+                .orElseGet(() -> EmptySchemaValidatorHolder.instance);
       }
       return new WorkflowApplication(this);
     }

impl/jackson/src/test/java/io/serverlessworkflow/impl/DateTimeDescriptorTest.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2020-Present The Serverless Workflow Specification 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 io.serverlessworkflow.impl;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import io.serverlessworkflow.impl.expressions.DateTimeDescriptor;
+import io.serverlessworkflow.impl.json.JsonUtils;
+import java.time.Instant;
+import org.junit.jupiter.api.Test;
+
+class DateTimeDescriptorTest {
+
+  @Test
+  void serializeDate() {
+    DateTimeDescriptor descriptor = DateTimeDescriptor.from(Instant.now());
+
+    JsonNode node = JsonUtils.fromValue(descriptor);
+    assertThat(node.get("iso8601").isTextual()).isTrue();
+    assertThat(node.get("epoch").isObject()).isTrue();
+  }
+}