diff --git a/datastore_server/source/java/ch/systemsx/cisd/openbis/dss/generic/shared/dto/Size.java b/datastore_server/source/java/ch/systemsx/cisd/openbis/dss/generic/shared/dto/Size.java
index bb239e6da8f5e6e9912583bb38221445951e745c..271abcd17d50130debca0d37d3925f8ab821286a 100644
--- a/datastore_server/source/java/ch/systemsx/cisd/openbis/dss/generic/shared/dto/Size.java
+++ b/datastore_server/source/java/ch/systemsx/cisd/openbis/dss/generic/shared/dto/Size.java
@@ -18,6 +18,11 @@ package ch.systemsx.cisd.openbis.dss.generic.shared.dto;
 
 public final class Size
 {
+    /**
+     * NULL_SIZE can be encode special conditions e.g. "no thumbnails available"
+     */
+    public final static Size NULL_SIZE = new Size(0, 0);
+
     private final int width;
 
     private final int height;