Addressed #16

Changed optional fields in HalLink to use java Optional.
Added HalLinkSerializer to fix odd issue where Optional is not serialized correctly despite jackson module.
Made indentation uniform

src/main/java/black/door/hate/HalLink.java

@@ -4,9 +4,14 @@
 import com.fasterxml.jackson.annotation.JsonIgnore;
 import com.fasterxml.jackson.annotation.JsonInclude;
 import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.core.JsonGenerator;
 import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.SerializerProvider;
+import com.fasterxml.jackson.databind.annotation.JsonSerialize;
+import com.fasterxml.jackson.databind.ser.std.StdSerializer;
 import lombok.*;
 
+import java.io.IOException;
 import java.net.URI;
 import java.net.URISyntaxException;
 import java.net.URL;
@@ -18,31 +23,31 @@
  */
 @Getter
 @EqualsAndHashCode
-@JsonInclude(JsonInclude.Include.NON_NULL)
+@JsonInclude(JsonInclude.Include.NON_EMPTY)
+@JsonSerialize(using = HalLink.HalLinkSerializer.class)
 public class HalLink implements LinkOrResource{
 
 	private @NonNull final String href;
 
 	@Getter(AccessLevel.NONE) @JsonProperty
 	private final Boolean templated;
-
-	private final String type;
-	private final URL deprecation;
-	private final String name;
-	private final URI profile;
-	private final String title;
-	private final String hreflang;
+	private final Optional<String> type;
+	private final Optional<URL> deprecation;
+	private final Optional<String> name;
+	private final Optional<URI> profile;
+	private final Optional<String> title;
+	private final Optional<String> hreflang;
 
 	@java.beans.ConstructorProperties({"href", "templated", "type", "deprecation", "name", "profile", "title", "hreflang"})
 	HalLink(String href, Boolean templated, String type, URL deprecation, String name, URI profile, String title, String hreflang) {
 		this.href = href;
 		this.templated = templated;
-		this.type = type;
-		this.deprecation = deprecation;
-		this.name = name;
-		this.profile = profile;
-		this.title = title;
-		this.hreflang = hreflang;
+		this.type = Optional.ofNullable(type);
+		this.deprecation = Optional.ofNullable(deprecation);
+		this.name = Optional.ofNullable(name);
+		this.profile = Optional.ofNullable(profile);
+		this.title = Optional.ofNullable(title);
+		this.hreflang = Optional.ofNullable(hreflang);
 	}
 
 	public static HalLinkBuilder builder() {
@@ -143,4 +148,38 @@ public HalLink build() {
 		}
 
 	}
+
+	public static class HalLinkSerializer extends StdSerializer<HalLink> {
+
+		protected HalLinkSerializer() {
+			this(HalLink.class);
+		}
+
+		protected HalLinkSerializer(Class<HalLink> clazz) {
+			super(clazz);
+		}
+
+		@Override
+		public void serialize(HalLink value, JsonGenerator gen, SerializerProvider provider) throws IOException {
+			gen.writeStartObject();
+
+			provider.defaultSerializeField("href", value.href, gen);
+			if(value.templated != null)
+				provider.defaultSerializeField("templated", value.templated, gen);
+			if(value.type.isPresent())
+				provider.defaultSerializeField("type", value.type, gen);
+			if(value.deprecation.isPresent())
+				provider.defaultSerializeField("deprecation", value.deprecation, gen);
+			if(value.name.isPresent())
+				provider.defaultSerializeField("name", value.name, gen);
+			if(value.profile.isPresent())
+				provider.defaultSerializeField("profile", value.profile, gen);
+			if(value.title.isPresent())
+				provider.defaultSerializeField("title", value.title, gen);
+			if(value.hreflang.isPresent())
+				provider.defaultSerializeField("hreflang", value.hreflang, gen);
+
+			gen.writeEndObject();
+		}
+	}
 }

src/main/java/black/door/hate/HalRepresentation.java

@@ -23,6 +23,7 @@
 import static black.door.hate.Constants.*;
 import static black.door.util.Misc.require;
 import static java.util.Map.Entry;
+import static java.util.Objects.requireNonNull;
 import static java.util.stream.Collectors.toList;
 import static java.util.stream.Collectors.toMap;
 
@@ -55,17 +56,12 @@ public class HalRepresentation implements java.io.Serializable {
 			Map<String, HalResource> embedded,
 			Map<String, List<HalResource>> multiEmbedded,
 			Map<String, Object> properties) {
-		require(null != links);
-		require(null != multiLinks);
-		require(null != embedded);
-		require(null != multiEmbedded);
-		require(null != properties);
-
-		this.links = links;
-		this.multiLinks = multiLinks;
-		this.embedded = embedded;
-		this.multiEmbedded = multiEmbedded;
-		this.properties = properties;
+
+		this.links = requireNonNull(links);
+		this.multiLinks = requireNonNull(multiLinks);
+		this.embedded = requireNonNull(embedded);
+		this.multiEmbedded = requireNonNull(multiEmbedded);
+		this.properties = requireNonNull(properties);
 	}
 
 	static ObjectMapper getMapper(){
@@ -130,8 +126,8 @@ protected HalRepresentationSerializer(Class<HalRepresentation> t) {
 
 		@Override
 		public void serialize(HalRepresentation halRepresentation,
-		                      JsonGenerator jsonGenerator,
-		                      SerializerProvider serializerProvider)
+							  JsonGenerator jsonGenerator,
+							  SerializerProvider serializerProvider)
 				throws IOException{
 			jsonGenerator.writeStartObject();
 
@@ -171,6 +167,7 @@ public void serialize(HalRepresentation halRepresentation,
 									.collect(toList())
 					));
 
+
 			//put all embedded resources and collections of embedded resources into one object
 			Map<String, Object> embedded = new HashMap<>();
 			embedded.putAll(embeddz);
@@ -266,7 +263,7 @@ public HalRepresentationBuilder addProperties(JsonNode jax){
 		 * @param multiRs
 		 */
 		private <T extends LinkOrResource> void add(String name, T res, Map<String, T> rs,
-		                                            Map<String, List<T>> multiRs){
+													Map<String, List<T>> multiRs){
 
 			if(res == null && ignoreNullResources)
 				return;

src/test/java/black/door/hate/HalLinkTest.java

@@ -1,6 +1,8 @@
 package black.door.hate;
 
 import com.damnhandy.uri.template.UriTemplate;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import lombok.val;
 import org.junit.Test;
@@ -14,13 +16,19 @@
  */
 public class HalLinkTest {
 
+	ObjectMapper mapper = new ObjectMapper()
+			.findAndRegisterModules();
+
 	@Test
-	public void testSerialization(){
+	public void testSerialization() throws JsonProcessingException {
 		val link = HalLink.builder()
 				.href(UriTemplate.fromTemplate("/~{username}"))
 				.build();
 
-		assertTrue(new ObjectMapper().valueToTree(link).get("templated").asBoolean());
+		JsonNode node = mapper.valueToTree(link);
+		assertTrue(node.get("templated").asBoolean());
+		assertFalse(node.has("name"));
+		System.out.println(mapper.writeValueAsString(link));
 	}
 
 	@Test