#653 - Polishing.

Expose nullability in Identifiable, ResourceSupport and Links via Optional.

src/main/java/org/springframework/hateoas/PagedResources.java

@@ -18,6 +18,7 @@ package org.springframework.hateoas;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.Optional;
 
 import javax.xml.bind.annotation.XmlAttribute;
 import javax.xml.bind.annotation.XmlRootElement;
@@ -105,7 +106,7 @@ public class PagedResources<T> extends Resources<T> {
 	 * @return
 	 */
 	@JsonIgnore
-	public Link getNextLink() {
+	public Optional<Link> getNextLink() {
 		return getLink(Link.REL_NEXT);
 	}
 
@@ -115,7 +116,7 @@ public class PagedResources<T> extends Resources<T> {
 	 * @return
 	 */
 	@JsonIgnore
-	public Link getPreviousLink() {
+	public Optional<Link> getPreviousLink() {
 		return getLink(Link.REL_PREVIOUS);
 	}
 
@@ -251,8 +252,8 @@ public class PagedResources<T> extends Resources<T> {
 		 */
 		@Override
 		public String toString() {
-			return String.format("Metadata { number: %d, total pages: %d, total elements: %d, size: %d }", number,
-					totalPages, totalElements, size);
+			return String.format("Metadata { number: %d, total pages: %d, total elements: %d, size: %d }", number, totalPages,
+					totalElements, size);
 		}
 
 		/*