Update javadoc.

See: #4184
See: #4197
Original pull request: #4203.

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

@@ -1326,9 +1326,10 @@ public interface MongoOperations extends FluentMongoOperations {
 	/**
 	 * Insert the object into the collection for the entity type of the object to save. <br />
 	 * The object is converted to the MongoDB native representation using an instance of {@see MongoConverter}. <br />
-	 * If your object has an "Id' property, it will be set with the generated Id from MongoDB. If your Id property is a
-	 * String then MongoDB ObjectId will be used to populate that string. Otherwise, the conversion from ObjectId to your
-	 * property type will be handled by Spring's BeanWrapper class that leverages Type Conversion API. See
+	 * If your object has an {@literal Id} property which holds a {@literal null} value, it will be set with the generated
+	 * Id from MongoDB. If your Id property is a String then MongoDB ObjectId will be used to populate that string.
+	 * Otherwise, the conversion from ObjectId to your property type will be handled by Spring's BeanWrapper class that
+	 * leverages Type Conversion API. See
 	 * <a href="https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#validation" > Spring's
 	 * Type Conversion"</a> for more details. <br />
 	 * Insert is used to initially store the object into the database. To update an existing object use the save method.

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

@@ -1093,9 +1093,10 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	/**
 	 * Insert the object into the collection for the entity type of the object to save. <br />
 	 * The object is converted to the MongoDB native representation using an instance of {@see MongoConverter}. <br />
-	 * If your object has an "Id' property, it will be set with the generated Id from MongoDB. If your Id property is a
-	 * String then MongoDB ObjectId will be used to populate that string. Otherwise, the conversion from ObjectId to your
-	 * property type will be handled by Spring's BeanWrapper class that leverages Type Conversion API. See
+	 * If your object has an {@literal Id} property which holds a {@literal null} value, it will be set with the generated
+	 * Id from MongoDB. If your Id property is a String then MongoDB ObjectId will be used to populate that string.
+	 * Otherwise, the conversion from ObjectId to your property type will be handled by Spring's BeanWrapper class that
+	 * leverages Type Conversion API. See
 	 * <a href="https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#validation" > Spring's
 	 * Type Conversion"</a> for more details. <br />
 	 * Insert is used to initially store the object into the database. To update an existing object use the save method.