diff --git a/site/app_model.php b/site/app_model.php
index 64c398b..12d1f58 100644
--- a/site/app_model.php
+++ b/site/app_model.php
@@ -39,6 +39,7 @@
 class AppModel extends Model {
 
   var $actsAs = array('Containable', 'Linkable');
+  var $useNullForEmpty = true;
 
   /**
    * Get Enum Values
@@ -131,6 +132,32 @@ class AppModel extends Model {
   }
 
 
+  function recursive_array_replace($find, $replace, &$data) {
+    if (!isset($data))
+      return;
+
+    if (is_array($data)) {
+      foreach ($data as $key => &$value) {
+	  $this->recursive_array_replace($find, $replace, $value);
+      }
+      return;
+    }
+
+    if (isset($replace))
+      $data = preg_replace($find, $replace, $data);
+    elseif (preg_match($find, $data))
+      $data = null;
+  }
+
+  function beforeSave() {
+    // Replace all empty strings with NULL.
+    // If a particular model doesn't like this, they'll have to
+    // override the behavior, or set useNullForEmpty to false.
+    if ($this->useNullForEmpty)
+      $this->recursive_array_replace("/^\s*$/", null, $this->data);
+    return true;
+  }
+
   /**************************************************************************
    **************************************************************************
    **************************************************************************