Direct Debit: add field CreditorReferenceID.

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

@@ -63,6 +63,7 @@ public class Invoice implements IExportableTransaction {
 	protected String specifiedProcuringProjectName = null;
 	protected String despatchAdviceReferencedDocumentID = null;
 	protected String vatDueDateTypeCode = null;
+	protected String creditorReferenceID; // required when direct debit is used.
 
 	public Invoice() {
 		ZFItems = new ArrayList<>();
@@ -878,4 +879,13 @@ public class Invoice implements IExportableTransaction {
 		return this;
 	}
 
+	public String getCreditorReferenceID() {
+		return creditorReferenceID;
+	}
+
+	public Invoice setCreditorReferenceID(String creditorReferenceID) {
+		this.creditorReferenceID = creditorReferenceID;
+		return this;
+	}
+
 }