java/OFErrorCauseData: fix regression

the new type did not have a default value which broke existing
floodlight unit tests.
diff --git a/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/OFErrorCauseData.java b/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/OFErrorCauseData.java
index b5c7af0..824b809 100644
--- a/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/OFErrorCauseData.java
+++ b/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/OFErrorCauseData.java
@@ -30,6 +30,12 @@
     private static final Logger logger =
             LoggerFactory.getLogger(OFErrorCauseData.class);
 
+    /** A default 'empty' cause. Note: the OFVersion OF_13 passed in here is irrelevant,
+     *  because parsing of the 0-byte array will always return null, irrespective of the
+     *  version.
+     */
+    public static final OFErrorCauseData NONE = new OFErrorCauseData(new byte[0], OFVersion.OF_13);
+
     private final byte[] data;
     private final OFVersion version;