Predis\ConnectionParameters::__isset() should check if a parameters has been set and its value is not null.

lib/Predis/ConnectionParameters.php

@@ -118,6 +118,10 @@ class ConnectionParameters implements IConnectionParameters {
     }
 
     public function __isset($parameter) {
+        return isset($this->_parameters[$parameter]);
+    }
+
+    public function setByUser($parameter) {
         return in_array($parameter, $this->_userDefined);
     }