Mapstruct: qualified by name null pointer exception

Question

When evaluating, match the fields using the get error method:

java.lang.NullPointerException: Cannot read the array length because "src" is null at java.base/java.util.Base64$Encoder.encode(Base64.java:291) ~[na:na] at java.base/java.util.Base64$Encoder.encodeToString(Base64.java:345) ~[na:na] at fqw.application.mapper.ResponseMapper.dataToBase64(ResponseMapper.java:31) ~[main/:na] .....

Mapper:

@Mapper
public interface ResponseMapper {

    ResponseMapper INSTANCE = Mappers.getMapper(ResponseMapper.class);

    @Mapping(target = "taskId", source = "id")
    @Mapping(target = "imageName", source = "imageMetadata.imageName")
    @Mapping(target = "imageData", source = "loadedImage.data",qualifiedByName = "dataToBase64")
    @Mapping(target = "imageResultData", source = "resultImage.data",qualifiedByName = "dataToBase64")
    @Mapping(target = "description", source = "imageMetadata.description")
    @Mapping(target = "contentType", source = "imageMetadata.contentType")
    ResponseDTO taskToResponseDTO(Task task);


    @Named("dataToBase64")
    default String dataToBase64(byte[] data){
        return Base64.getEncoder().encodeToString(data);
    }
}

what could be the problem?

Answer 1

To simplify the question, run this line of code first (you'll get the same error):

Base64.getEncoder().encodeToString(null);
// java.lang.NullPointerException: Cannot read the array length because "src" is null

An easy fix would be a simple null check - but you need to decide what do you want to do if the parameter is null. here are some options:

String dataToBase64(byte[] data){
    if(Objects.isNull(data)) {
        data = new byte[0];
    }
    return Base64.getEncoder().encodeToString(data);
}

String dataToBase64(byte[] data){
    if(Objects.isNull(data)) {
        return null;
    }
    return Base64.getEncoder().encodeToString(data);
}

Optional<String> dataToBase64(byte[] data){
    return Optional.ofNullable(data)
        .map(Base64.getEncoder()::encodeToString);
}