Use Jdk8Module to serialize Optional values

pom.xml

@@ -86,6 +86,11 @@
         <artifactId>jackson-dataformat-yaml</artifactId>
         <version>2.14.0</version>
       </dependency>
+      <dependency>
+        <groupId>com.fasterxml.jackson.datatype</groupId>
+        <artifactId>jackson-datatype-jdk8</artifactId>
+        <version>2.14.0</version>
+      </dependency>
     </dependencies>
   </dependencyManagement>
 
@@ -150,6 +155,10 @@
       <groupId>com.fasterxml.jackson.dataformat</groupId>
       <artifactId>jackson-dataformat-yaml</artifactId>
     </dependency>
+    <dependency>
+      <groupId>com.fasterxml.jackson.datatype</groupId>
+      <artifactId>jackson-datatype-jdk8</artifactId>
+    </dependency>
     <dependency>
       <groupId>ch.obermuhlner</groupId>
       <artifactId>big-math</artifactId>

src/main/java/com/hubspot/jinjava/JinjavaConfig.java

@@ -19,6 +19,7 @@
 
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.PropertyNamingStrategies;
+import com.fasterxml.jackson.datatype.jdk8.Jdk8Module;
 import com.google.common.collect.ImmutableSet;
 import com.hubspot.jinjava.el.JinjavaInterpreterResolver;
 import com.hubspot.jinjava.el.JinjavaObjectUnwrapper;
@@ -158,7 +159,7 @@ private JinjavaConfig(Builder builder) {
 
   private ObjectMapper setupObjectMapper(@Nullable ObjectMapper objectMapper) {
     if (objectMapper == null) {
-      objectMapper = new ObjectMapper();
+      objectMapper = new ObjectMapper().registerModule(new Jdk8Module());
       if (legacyOverrides.isUseSnakeCasePropertyNaming()) {
         objectMapper.setPropertyNamingStrategy(PropertyNamingStrategies.SNAKE_CASE);
       }

src/main/java/com/hubspot/jinjava/objects/serialization/PyishSerializable.java

@@ -6,6 +6,7 @@
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.ObjectWriter;
 import com.fasterxml.jackson.databind.SerializerProvider;
+import com.fasterxml.jackson.datatype.jdk8.Jdk8Module;
 import com.google.common.annotations.Beta;
 import com.hubspot.jinjava.interpret.DeferredValueException;
 import com.hubspot.jinjava.objects.PyWrapper;
@@ -19,6 +20,7 @@ public interface PyishSerializable extends PyWrapper {
   ObjectWriter SELF_WRITER = new ObjectMapper(
     new JsonFactoryBuilder().quoteChar('\'').build()
   )
+    .registerModule(new Jdk8Module())
     .writer(PyishPrettyPrinter.INSTANCE)
     .with(PyishCharacterEscapes.INSTANCE);
 

src/test/java/com/hubspot/jinjava/util/EagerExpressionResolverTest.java

@@ -35,6 +35,7 @@
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Optional;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.atomic.AtomicLong;
 import org.junit.After;
@@ -93,6 +94,15 @@ private JinjavaInterpreter getInterpreter(boolean evaluateMapKeys) throws Except
           this.getClass().getDeclaredMethod("sleeper")
         )
       );
+    jinjava
+      .getGlobalContext()
+      .registerFunction(
+        new ELFunctionDefinition(
+          "",
+          "optionally",
+          this.getClass().getDeclaredMethod("optionally", boolean.class)
+        )
+      );
     interpreter = new JinjavaInterpreter(jinjava.newInterpreter());
     context = interpreter.getContext();
     context.put("deferred", DeferredValue.instance());
@@ -124,6 +134,14 @@ public void itResolvesDeferredBoolean() {
     assertThat(interpreter.resolveELExpression(partiallyResolved, 1)).isEqualTo(true);
   }
 
+  @Test
+  public void itSerializesNestedOptional() {
+    assertThat(eagerResolveExpression("[optionally(true)]").toString())
+      .isEqualTo("['1'|allow_snake_case]");
+    assertThat(eagerResolveExpression("[optionally(false)]").toString())
+      .isEqualTo("[null|allow_snake_case]");
+  }
+
   @Test
   public void itResolvesDeferredList() {
     context.put("foo", "foo_val");
@@ -877,6 +895,10 @@ public static long sleeper() throws InterruptedException {
     return sleepTime;
   }
 
+  public static Optional<String> optionally(boolean hasValue) {
+    return Optional.of(hasValue).filter(Boolean::booleanValue).map(ignored -> "1");
+  }
+
   private static class Foo {
 
     private final String bar;