Merge pull request #97 from defalt2111/bugfix_birthday_string_can't_be_null

bugfix. while setting identity type, it was previously not possible to be an entity seller

Author: JohannesRabauer

bzst-dip-java-client/src/main/java/software/xdev/bzst/dip/client/model/message/BzstDipCorrectableReportableSellerType.java

@@ -51,7 +51,7 @@ public CorrectableReportableSellerType toXmlType(final BzstDipConfiguration conf
 			this.vat,
 			this.firstName,
 			this.lastName,
-			this.birthDate.format(DateTimeFormatter.ISO_LOCAL_DATE),
+			this.birthDate == null ? "NULL" : this.birthDate.format(DateTimeFormatter.ISO_LOCAL_DATE),
 			this.legalAddress.toXmlType(),
 			this.addressFix.toXmlType(),
 			this.numberOfActivities.toXmlType(),