DATAMONGO-1728 - Fix NPE in ExecutableFindOperation.first().

Original pull request: #476.

Author: christophstrobl

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/ExecutableFindOperationSupport.java

@@ -186,8 +186,7 @@ static class DelegatingQueryCursorPreparer implements CursorPreparer {
 		@Override
 		public FindIterable<Document> prepare(FindIterable<Document> cursor) {
 
-			FindIterable<Document> target = delegate.prepare(cursor);
-
+			FindIterable<Document> target = delegate != null ? delegate.prepare(cursor) : cursor;
 			return limit.map(target::limit).orElse(target);
 		}
 

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/ExecutableFindOperationSupportTests.java

@@ -213,6 +213,11 @@ public void findAllNearByWithCollectionAndProjection() {
 		assertThat(results.getContent().get(0).getContent().getId()).isEqualTo("alderan");
 	}
 
+	@Test // DATAMONGO-1728
+	public void firstShouldReturnFirstEntryInCollection() {
+		assertThat(template.query(Person.class).first()).isNotEmpty();
+	}
+
 	@Data
 	@org.springframework.data.mongodb.core.mapping.Document(collection = STAR_WARS)
 	static class Person {