diff --git a/Backend/services/core/src/main/java/org/edu_sharing/repository/server/MCAlfrescoAPIClient.java b/Backend/services/core/src/main/java/org/edu_sharing/repository/server/MCAlfrescoAPIClient.java
index 874aa3868..8924c7edf 100644
--- a/Backend/services/core/src/main/java/org/edu_sharing/repository/server/MCAlfrescoAPIClient.java
+++ b/Backend/services/core/src/main/java/org/edu_sharing/repository/server/MCAlfrescoAPIClient.java
@@ -602,7 +602,7 @@ protected String getValue(String type, String prop, Object _value, String metada
 			return result;
 		} else if (_value instanceof List && ((List) _value).size() == 0) {
 			// cause empty list toString returns "[]"
-			return "";
+			return null;
 		} else if (_value instanceof String) {
 			return (String) _value;
 		} else if (_value instanceof Number) {