diff --git a/ext/memory/src/main/java/org/minimalj/repository/memory/InMemoryRepository.java b/ext/memory/src/main/java/org/minimalj/repository/memory/InMemoryRepository.java
index <HASH>..<HASH> 100644
--- a/ext/memory/src/main/java/org/minimalj/repository/memory/InMemoryRepository.java
+++ b/ext/memory/src/main/java/org/minimalj/repository/memory/InMemoryRepository.java
@@ -179,9 +179,9 @@ public class InMemoryRepository implements Repository {
 				Object value = field.get(object);
 				if (field.getAnnotation(NotEmpty.class) != null) {
 					if (value == null) {
-						throw new IllegalArgumentException();
+						throw new IllegalArgumentException(field.getName() + " must not be null");
 					} else if (value instanceof String && ((String)value).isEmpty()) {
-						throw new IllegalArgumentException();
+						throw new IllegalArgumentException(field.getName() + " must not be empty");
 					}
 				}
InMemoryRepository: more meaningful exceptions for invalid fields