Index: tests/Zend/Validate/File/UploadTest.php
===================================================================
--- tests/Zend/Validate/File/UploadTest.php	(revision 23564)
+++ tests/Zend/Validate/File/UploadTest.php	(working copy)
@@ -252,6 +252,18 @@
         $validator->setFiles($files);
         $this->assertEquals($files, $validator->getFiles());
     }
+    
+    /**
+     * @group ZF-10738
+     */
+    public function testSetFilesNull()
+    {
+        $_FILES = NULL;
+        $validator = new Zend_Validate_File_Upload();
+        $validator->setFiles(NULL);
+        $this->assertEquals(array(), $validator->getFiles());
+    }
+
 }
 
 // Call Zend_Validate_File_UploadTest::main() if this source file is executed directly.
Index: library/Zend/Validate/File/Upload.php
===================================================================
--- library/Zend/Validate/File/Upload.php	(revision 23564)
+++ library/Zend/Validate/File/Upload.php	(working copy)
@@ -101,13 +101,15 @@
     {
         if ($file !== null) {
             $return = array();
-            foreach ($this->_files as $name => $content) {
-                if ($name === $file) {
-                    $return[$file] = $this->_files[$name];
-                }
-
-                if ($content['name'] === $file) {
-                    $return[$name] = $this->_files[$name];
+            if (is_array($this->_files)) {
+                foreach ($this->_files as $name => $content) {
+                    if ($name === $file) {
+                        $return[$file] = $this->_files[$name];
+                    }
+    
+                    if ($content['name'] === $file) {
+                        $return[$name] = $this->_files[$name];
+                    }
                 }
             }
 
@@ -130,15 +132,19 @@
      */
     public function setFiles($files = array())
     {
-        if (count($files) === 0) {
-            $this->_files = $_FILES;
-        } else {
+        if (is_array($files) && count($files) > 0) {
             $this->_files = $files;
+        } elseif (is_array($_FILES)) {
+            $this->_files = $_FILES;
+        } else { 
+            $this->_files = array();
         }
 
-        foreach($this->_files as $file => $content) {
-            if (!isset($content['error'])) {
-                unset($this->_files[$file]);
+        if (is_array($this->_files)) {
+            foreach($this->_files as $file => $content) {
+                if (!isset($content['error'])) {
+                    unset($this->_files[$file]);
+                }
             }
         }
 
@@ -157,16 +163,20 @@
     public function isValid($value, $file = null)
     {
         $this->_messages = null;
-        if (array_key_exists($value, $this->_files)) {
-            $files[$value] = $this->_files[$value];
-        } else {
-            foreach ($this->_files as $file => $content) {
-                if (isset($content['name']) && ($content['name'] === $value)) {
-                    $files[$file] = $this->_files[$file];
-                }
+        $files = array();
 
-                if (isset($content['tmp_name']) && ($content['tmp_name'] === $value)) {
-                    $files[$file] = $this->_files[$file];
+        if (is_array($this->_files)) {
+            if (array_key_exists($value, $this->_files)) {
+                $files[$value] = $this->_files[$value];
+            } else {
+                foreach ($this->_files as $file => $content) {
+                    if (isset($content['name']) && ($content['name'] === $value)) {
+                        $files[$file] = $this->_files[$file];
+                    }
+    
+                    if (isset($content['tmp_name']) && ($content['tmp_name'] === $value)) {
+                        $files[$file] = $this->_files[$file];
+                    }
                 }
             }
         }