skip verification if file doesn not exist

dvc/output/local.py

@@ -72,6 +72,9 @@ class OutputLOCAL(DependencyLOCAL):
         if not self.metric:
             return
 
+        if not os.path.exists(self.path):
+            return
+
         if os.path.isdir(self.path):
             msg = 'Directory \'{}\' cannot be used as metrics.'
             raise DvcException(msg.format(self.rel_path))

dvc/project.py

@@ -1023,9 +1023,6 @@ class Project(object):
         self._metrics_modify(path, typ, xpath)
 
     def metrics_add(self, path, typ=None, xpath=None):
-        if not os.path.exists(path):
-            raise DvcException('File does not exist'.format(path))
-
         if not typ:
             typ = 'raw'
         self._metrics_modify(path, typ, xpath)