diff --git a/authentication/source/java/ch/systemsx/cisd/authentication/Principal.java b/authentication/source/java/ch/systemsx/cisd/authentication/Principal.java
index eb0df3b9a973b0cdad5a7413aef04df316be290a..c111e1d0a57c5c8944067933f1c9c3ac9f4ef2c0 100644
--- a/authentication/source/java/ch/systemsx/cisd/authentication/Principal.java
+++ b/authentication/source/java/ch/systemsx/cisd/authentication/Principal.java
@@ -132,7 +132,7 @@ public final class Principal extends AbstractHashable implements Serializable
      */
     public final String getProperty(final String key)
     {
-        return properties.get(key);
+        return (properties != null) ? properties.get(key) : null;
     }
 
     /** Retuns an unmodifiable <code>Set</code> of present properties. */