Mapper:

```
public static ObjectMapper mapper = new ObjectMapper()
            .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
            .setVisibility(PropertyAccessor.FIELD, JsonAutoDetect.Visibility.ANY)
            .enable(SerializationFeature.INDENT_OUTPUT);

```

Class to serialize:

```
@Builder(builderClassName = "GooglePlayGameBuilder", toBuilder = true)
@JsonDeserialize(builder = GooglePlayGame.GooglePlayGameBuilder.class)
public final class GooglePlayGame  {

    @JsonProperty("Title") private final String title;
    @JsonProperty("Genre") private final String genre;
    @JsonProperty("Price") private final String price;
    @JsonProperty("Last updated") private final String lastUpdated;
    @JsonProperty("Current version") private final String currentVersion;
    @JsonProperty("Requirements") private final String requiresAndroid;
    @JsonProperty("IAP") private final String IAP;
    @JsonProperty("Contacts") private final String devEmail;

...

```

Add object to map and then i want to serialize my map:

```
public static volatile ConcurrentMap<String, GooglePlayGame> games = new ConcurrentSkipListMap<>(String.CASE_INSENSITIVE_ORDER);

```

Write to file:

```
public static void saveLibraryToFile(){
        try {
            mapper.writeValue(new File(LIBRARY_FILENAME), games);
        } catch (IOException e) {
            log.error("[Couldn't write to file] ", e.getMessage());
        }
    }

```

After this my JSON looks like:

```
{
  "Never Alone: Ki Edition" : {
    "Title" : "Never Alone: Ki Edition",
    "Genre" : "Adventures",
    "Price" : "4,99 €",
    "Last updated" : "September 15, 2016",
    "Current version" : "1.0.0",
    "Requirements" : "2.3+",
    "IAP" : "nope",
    "Contacts" : "support@neveralonegame.com"
  },
...

```

If i will annotate my class with lombok @Getter strange field will appear:

```
{
  "Never Alone: Ki Edition" : {
    "iap" : "nope"
    "Title" : "Never Alone: Ki Edition",
    "Genre" : "Adventures",
    "Price" : "4,99 €",
    "Last updated" : "September 15, 2016",
    "Current version" : "1.0.0",
    "Requirements" : "2.3+",
    "IAP" : "nope",
    "Contacts" : "support@neveralonegame.com"
  },

```

I dont understand this field: 

```
"iap" : "nope"

```

From where Jackson found it? 
I checked my local map with logs and all fine, this field doesnt exist, but during serialization it appears.