1 files changed, 3 insertions, 2 deletions
diff --git a/src/main/java/com/c2kernel/graph/model/GraphableVertex.java b/src/main/java/com/c2kernel/graph/model/GraphableVertex.java
index 77be7a8..b0b74fd 100644
--- a/src/main/java/com/c2kernel/graph/model/GraphableVertex.java
+++ b/src/main/java/com/c2kernel/graph/model/GraphableVertex.java
@@ -26,10 +26,11 @@ public abstract class GraphableVertex extends Vertex
 	{
 		return mProperties;
 	}
-	protected int getVersionNumberProperty(String propName) throws InvalidDataException {
+	protected Integer getVersionNumberProperty(String propName) throws InvalidDataException {
 		Object val = getProperties().get(propName);
+		if (val == null || val.equals("") || val.toString().equals("-1")) return null;
 		try {
-			return Integer.parseInt(val.toString());
+			return new Integer(val.toString());
 		} catch (NumberFormatException ex) {
 			throw new InvalidDataException("Invalid version number for property '"+propName+"': "+val.toString(), "");
 		}