GUACAMOLE-678: Return null for null property values.
diff --git a/guacamole-ext/src/main/java/org/apache/guacamole/properties/URIGuacamoleProperty.java b/guacamole-ext/src/main/java/org/apache/guacamole/properties/URIGuacamoleProperty.java
index d40f91e..7f53bf8 100644
--- a/guacamole-ext/src/main/java/org/apache/guacamole/properties/URIGuacamoleProperty.java
+++ b/guacamole-ext/src/main/java/org/apache/guacamole/properties/URIGuacamoleProperty.java
@@ -32,6 +32,10 @@
     @Override
     public URI parseValue(String value) throws GuacamoleException {
         
+        // If nothing is provided, just return null.
+        if (value == null)
+            return null;
+        
         try {
             return new URI(value);
         }