new bean constructor

library/src/main/java/org/mustangproject/DesignatedProductClassification.java

@@ -31,7 +31,7 @@ import org.mustangproject.ZUGFeRD.IDesignatedProductClassification;
 @JsonIgnoreProperties(ignoreUnknown = true)
 @JsonInclude(JsonInclude.Include.NON_EMPTY)
 public class DesignatedProductClassification implements IDesignatedProductClassification {
-	private final ClassCode classCode;
+	private ClassCode classCode;
 	private String className;
 
 	/**
@@ -54,6 +54,13 @@ public class DesignatedProductClassification implements IDesignatedProductClassi
 		this(classCode, null);
 	}
 
+	/**
+	 * Bean constructor for schemed product descriptor
+	 */
+	public DesignatedProductClassification() {
+		classCode = null;// we need this constructor for jackson, i.e. to be able to JSON
+	}
+
 	@Override
 	public ClassCode getClassCode() {
 		return classCode;