DATAES-363 - Fixed CrudRepository.existsById(…) implementation.

Properly use Optional.isPresent() over a null check.

Original pull request: spring-projects#183.

Author: michael-wirth

src/main/java/org/springframework/data/elasticsearch/repository/support/AbstractElasticsearchRepository.java

@@ -55,6 +55,7 @@
  * @author Kevin Leturc
  * @author Mark Paluch
  * @author Christoph Strobl
+ * @author Michael Wirth
  */
 public abstract class AbstractElasticsearchRepository<T, ID extends Serializable>
 		implements ElasticsearchRepository<T, ID> {
@@ -188,7 +189,7 @@ public <S extends T> Iterable<S> saveAll(Iterable<S> entities) {
 
 	@Override
 	public boolean existsById(ID id) {
-		return findById(id) != null;
+		return findById(id).isPresent();
 	}
 
 	@Override

src/test/java/org/springframework/data/elasticsearch/repository/support/SimpleElasticsearchRepositoryTests.java

@@ -47,6 +47,7 @@
  * @author Mohsin Husen
  * @author Mark Paluch
  * @author Christoph Strobl
+ * @author Michael Wirth
  */
 @RunWith(SpringJUnit4ClassRunner.class)
 @ContextConfiguration("classpath:/simple-repository-test.xml")
@@ -274,6 +275,18 @@ public void shouldReturnTrueGivenDocumentWithIdExists() {
 		assertEquals(exist, true);
 	}
 
+	@Test // DATAES-363
+	public void shouldReturnFalseGivenDocumentWithIdDoesNotExist() {
+		// given
+		String documentId = randomNumeric(5);
+
+		// when
+		boolean exist = repository.existsById(documentId);
+
+		// then
+		assertEquals(exist, false);
+	}
+
 	@Test
 	public void shouldReturnResultsForGivenSearchQuery() {
 		// given

src/test/java/org/springframework/data/elasticsearch/repository/support/UUIDElasticsearchRepositoryTests.java

@@ -45,6 +45,7 @@
  * @author Mohsin Husen
  * @author Mark Paluch
  * @author Christoph Strobl
+ * @author Michael Wirth
  */
 @RunWith(SpringJUnit4ClassRunner.class)
 @ContextConfiguration("classpath:/simple-repository-test.xml")
@@ -262,6 +263,18 @@ public void shouldReturnTrueGivenDocumentWithIdExists() {
 		assertEquals(exist, true);
 	}
 
+	@Test // DATAES-363
+	public void shouldReturnFalseGivenDocumentWithIdDoesNotExist() {
+		// given
+		UUID documentId = UUID.randomUUID();
+
+		// when
+		boolean exist = repository.existsById(documentId);
+
+		// then
+		assertEquals(exist, false);
+	}
+
 	@Test
 	public void shouldDeleteAll() {
 		// when