Treat a blank identifier as null

src/main/java/org/qortal/arbitrary/ArbitraryDataReader.java

@@ -58,6 +58,11 @@ public class ArbitraryDataReader {
             resourceId = resourceId.toLowerCase();
         }
 
+        // If identifier is a blank string, treat it as null
+        if (identifier == "") {
+            identifier = null;
+        }
+
         this.resourceId = resourceId;
         this.resourceIdType = resourceIdType;
         this.service = service;

src/main/java/org/qortal/data/transaction/ArbitraryTransactionData.java

@@ -182,7 +182,7 @@ public class ArbitraryTransactionData extends TransactionData {
 	}
 
 	public String getIdentifier() {
-		return this.identifier;
+		return (this.identifier != "") ? this.identifier : null;
 	}
 
 	public Method getMethod() {