public class AirEventInput {

private Long id;
private String eventName;
private Long startDate;
private Long endDate;

public Long getId() {
    return id;
}

public void setId(Long id) {
    this.id = id;
}

public String getEventName() {
    return eventName;
}

public void setEventName(String eventName) {
    this.eventName = eventName;
}

public Long getStartDate() {
    return startDate;
}

public void setStartDate(Long startDate) {
    this.startDate = startDate;
}

public Long getEndDate() {
    return endDate;
}

public void setEndDate(Long endDate) {
    this.endDate = endDate;
}

public class AirEventAPI {

private Long id;
private String eventName;
private Long startDate;
private Long endDate;

public Long getId() {
    return id;
}

public void setId(Long id) {
    this.id = id;
}

public String getEventName() {
    return eventName;
}

public void setEventName(String eventName) {
    this.eventName = eventName;
}

public Long getStartDate() {
    return startDate;
}

public void setStartDate(Long startDate) {
    this.startDate = startDate;
}

public Long getEndDate() {
    return endDate;
}

public void setEndDate(Long endDate) {
    this.endDate = endDate;
}

public EventAPI mergeTwoEvents(EventInput eventInput, EventAPI eventAPI){
    ModelMapper modelMapper = new ModelMapper();
    modelMapper.createTypeMap(EventInput.class, EventAPI.class)
               .addMappings((mapper) -> mapper.skip(AirEventAPI::setStartDate));
               .setCondition(Conditions.isNotNull());


    modelMapper.map(eventInput, eventAPI);

    return eventAPI;
}