diff --git a/openbis/source/java/ch/ethz/sis/openbis/generic/server/asapi/v3/executor/entity/AbstractUpdateEntityToOneRelationExecutor.java b/openbis/source/java/ch/ethz/sis/openbis/generic/server/asapi/v3/executor/entity/AbstractUpdateEntityToOneRelationExecutor.java
index 05d24eb4ab246bbf542e664b4db941f14c518a90..0f55c60dfd1e1ae19ec5057f31731ac8e16a4202 100644
--- a/openbis/source/java/ch/ethz/sis/openbis/generic/server/asapi/v3/executor/entity/AbstractUpdateEntityToOneRelationExecutor.java
+++ b/openbis/source/java/ch/ethz/sis/openbis/generic/server/asapi/v3/executor/entity/AbstractUpdateEntityToOneRelationExecutor.java
@@ -118,7 +118,10 @@ public abstract class AbstractUpdateEntityToOneRelationExecutor<ENTITY_UPDATE, E
                         check(context, entity, relatedId, related);
                         update(context, entity, related);
                         allAdded.add(related);
-                        allRemoved.add(currentlyRelated);
+                        if (currentlyRelated != null)
+                        {
+                            allRemoved.add(currentlyRelated);
+                        }
                     }
                 }