DATAMONGO-2661 - Polishing.

Add ticket reference.

Original pull request: #894.

spring-data-mongodb/src/test/kotlin/org/springframework/data/mongodb/core/query/KPropertyPathTests.kt

@@ -93,7 +93,7 @@ class KPropertyPathTests {
 		assertThat(property).isEqualTo("entity.book.author.name")
 	}
 
-	@Test
+	@Test // DATAMONGO-2661
 	fun `Convert nullable KProperty to field name`() {
 		class Cat(val name: String)
 		class Owner(val cat: Cat?)