gn.py dies with exception when it can't find buildtools/

gclient_utils.py

Index: gclient_utils.py
diff --git a/gclient_utils.py b/gclient_utils.py
index f80cd78e4a52e6ebb4abe5ab2fa35203191a9ce3..de1b0422023b2c59370734b39c3c20208908816e 100644
--- a/gclient_utils.py
+++ b/gclient_utils.py
@@ -698,6 +698,8 @@ def GetBuildtoolsPath():
     return override
 
   primary_solution = GetPrimarySolutionPath()
+  if primary_solution is None:
+    return None
   buildtools_path = os.path.join(primary_solution, 'buildtools')
   if not os.path.exists(buildtools_path):
     # Buildtools may be in the gclient root.