diff --git a/openbis/source/java/ch/ethz/sis/openbis/generic/server/asapi/v3/executor/sample/SetSampleExperimentExecutor.java b/openbis/source/java/ch/ethz/sis/openbis/generic/server/asapi/v3/executor/sample/SetSampleExperimentExecutor.java
index ee411ddba4911f11b66d3b6daba352b5000b8b6a..5089a8b71fb0c8eda85f9bf199630fbfba429229 100644
--- a/openbis/source/java/ch/ethz/sis/openbis/generic/server/asapi/v3/executor/sample/SetSampleExperimentExecutor.java
+++ b/openbis/source/java/ch/ethz/sis/openbis/generic/server/asapi/v3/executor/sample/SetSampleExperimentExecutor.java
@@ -48,7 +48,10 @@ public class SetSampleExperimentExecutor extends AbstractSetEntityExperimentRela
     @Override
     protected void set(IOperationContext context, SamplePE entity, ExperimentPE related)
     {
-        relationshipService.assignSampleToExperiment(context.getSession(), entity, related);
+        if (related != null)
+        {
+            relationshipService.assignSampleToExperiment(context.getSession(), entity, related);
+        }
     }
 
 }
diff --git a/openbis/source/java/ch/ethz/sis/openbis/generic/server/asapi/v3/executor/sample/SetSampleProjectExecutor.java b/openbis/source/java/ch/ethz/sis/openbis/generic/server/asapi/v3/executor/sample/SetSampleProjectExecutor.java
index 3ec400493db469ac5aa81e03a0bf185862f85c6d..0532c8cc72a27bf3ca2244fb0def9390c67a985c 100644
--- a/openbis/source/java/ch/ethz/sis/openbis/generic/server/asapi/v3/executor/sample/SetSampleProjectExecutor.java
+++ b/openbis/source/java/ch/ethz/sis/openbis/generic/server/asapi/v3/executor/sample/SetSampleProjectExecutor.java
@@ -75,7 +75,10 @@ public class SetSampleProjectExecutor extends AbstractSetEntityToOneRelationExec
     @Override
     protected void set(IOperationContext context, SamplePE entity, ProjectPE related)
     {
-        relationshipService.assignSampleToProject(context.getSession(), entity, related);
+        if (related != null)
+        {
+            relationshipService.assignSampleToProject(context.getSession(), entity, related);
+        }
     }
 
 }