Extensions Docs Server: Uniform handling of file not found errors

chrome/common/extensions/docs/server2/server_instance.py

Index: chrome/common/extensions/docs/server2/server_instance.py
diff --git a/chrome/common/extensions/docs/server2/server_instance.py b/chrome/common/extensions/docs/server2/server_instance.py
index 2fa2a953c5b4bbce80b7d23d5c2c48eecfec9001..7c1294fee19d3ea6d5a281815fe73cba2ac2a692 100644
--- a/chrome/common/extensions/docs/server2/server_instance.py
+++ b/chrome/common/extensions/docs/server2/server_instance.py
@@ -6,6 +6,8 @@ from fnmatch import fnmatch
 import mimetypes
 import os
 
+from file_system import FileNotFoundError
+
 STATIC_DIR_PREFIX = 'docs/server2'
 DOCS_PATH = 'docs'
 
@@ -30,8 +32,8 @@ class ServerInstance(object):
       base, ext = os.path.splitext(path)
       response.headers['content-type'] = mimetypes.types_map[ext]
       return result
-    except Exception:
-      return ''
+    except FileNotFoundError:
+      return None
 
   def Get(self, path, request, response):
     templates = self._template_data_source_factory.Create(request)