diff --git a/openbis/source/java/ch/systemsx/cisd/openbis/generic/shared/dto/SamplePE.java b/openbis/source/java/ch/systemsx/cisd/openbis/generic/shared/dto/SamplePE.java
index b8e0d5adef54ca86ea08e97cae2b6c4354c78972..4910dc9a88c4ed7ac256b2db63a21b095c38dec0 100644
--- a/openbis/source/java/ch/systemsx/cisd/openbis/generic/shared/dto/SamplePE.java
+++ b/openbis/source/java/ch/systemsx/cisd/openbis/generic/shared/dto/SamplePE.java
@@ -337,7 +337,6 @@ public class SamplePE implements IIdAndCodeHolder, Comparable<SamplePE>,
     }
 
     @ManyToOne(fetch = FetchType.LAZY)
-    @NotNull(message = ValidationMessages.EXPERIMENT_NOT_NULL_MESSAGE)
     @JoinColumn(name = ColumnNames.EXPERIMENT_COLUMN, updatable = true)
     @IndexedEmbedded(prefix = SearchFieldConstants.PREFIX_EXPERIMENT)
     private ExperimentPE getExperimentInternal()
diff --git a/openbis/source/sql/postgresql/migration/migration-031-032.sql b/openbis/source/sql/postgresql/migration/migration-031-032.sql
index d5f42cba773d2ac281d12f1e225f2f50692ab888..2e1532900d4a030777c1ba85b634c3a7f4e0eb03 100644
--- a/openbis/source/sql/postgresql/migration/migration-031-032.sql
+++ b/openbis/source/sql/postgresql/migration/migration-031-032.sql
@@ -61,8 +61,6 @@ DROP SEQUENCE procedure_type_id_seq;
 --  Purpose:  Replace trigger SAMPLE_CODE_UNIQUENESS_CHECK 
 ------------------------------------------------------------------------------------
 
-DROP FUNCTION SAMPLE_CODE_UNIQUENESS_CHECK();
-
 CREATE OR REPLACE FUNCTION SAMPLE_CODE_UNIQUENESS_CHECK() RETURNS trigger AS $$
 DECLARE
    counter  INTEGER;