[2.0] Fixed issue with Proxy classes that was silently failing to load correspondent Entity.

lib/Doctrine/ORM/EntityNotFoundException.php

+<?php
+
+namespace Doctrine\ORM;
+
+/**
+ * Exception thrown when a Proxy fails to retrieve an Entity result.
+ *
+ * @author robo
+ * @since 2.0
+ */
+class EntityNotFoundException extends ORMException
+{
+    public function __construct()
+    {
+        parent::__construct('Entity was found although one item was expected.');
+    }
+}
\ No newline at end of file

lib/Doctrine/ORM/Proxy/ProxyFactory.php

@@ -257,7 +257,9 @@ namespace <namespace> {
         private function _load() {
             if (!$this->__isInitialized__ && $this->_entityPersister) {
                 $this->__isInitialized__ = true;
-                $this->_entityPersister->load($this->_identifier, $this);
+                if ($this->_entityPersister->load($this->_identifier, $this) === null) {
+                    throw new \Doctrine\ORM\EntityNotFoundException();
+                }
                 unset($this->_entityPersister);
                 unset($this->_identifier);
             }