Not able to serialize a Map

[riteshsingh2204]

Exception in thread "main" pl.zientarski.MappingException: Could not serialize type:java.util.Map<java.lang.String, java.lang.String>
at pl.zientarski.serialization.GenericObjectSerializer.toJsonObject(GenericObjectSerializer.java:26)
at pl.zientarski.typehandler.DefaultTypeHandler.lambda$addProperties$16(DefaultTypeHandler.java:58)
at java.util.HashMap$KeySpliterator.forEachRemaining(HashMap.java:1556)
at java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:580)
at pl.zientarski.typehandler.DefaultTypeHandler.addProperties(DefaultTypeHandler.java:58)
at pl.zientarski.typehandler.DefaultTypeHandler.process(DefaultTypeHandler.java:38)
at pl.zientarski.SchemaMapper.toJsonSchema4(SchemaMapper.java:78)
at pl.zientarski.SchemaMapper.toJsonSchema4(SchemaMapper.java:71)
at pl.zientarski.SchemaMapper.lambda$toJsonSchema4$2(SchemaMapper.java:95)
at java.util.Iterator.forEachRemaining(Iterator.java:116)
at pl.zientarski.SchemaMapper.toJsonSchema4(SchemaMapper.java:94)

Class:
@DaTa
public class ValidationAttributes implements Serializable {
private static final long serialVersionUID = -2218823081401507225L;
private String configObjectType;
private String configObjectId;
private String configObjectName;
private Map<String, String> configAttributes;

public ValidationAttributes() {
configAttributes = new HashMap<>();
}
}