upload.py: honor explicit empty title

R=pauljensen@chromium.org
BUG=
TEST=PatchSet 3 of this CL

Review-Url: https://codereview.chromium.org/2096123003

git_cl.py

@@ -1898,7 +1898,7 @@ class _RietveldChangelistImpl(_ChangelistCodereviewBase):
       upload_args.extend(['--email', options.email])
 
     if self.GetIssue():
-      if options.title:
+      if options.title is not None:
         upload_args.extend(['--title', options.title])
       if options.message:
         upload_args.extend(['--message', options.message])
@@ -1906,7 +1906,7 @@ class _RietveldChangelistImpl(_ChangelistCodereviewBase):
       print('This branch is associated with issue %s. '
             'Adding patch to that issue.' % self.GetIssue())
     else:
-      if options.title:
+      if options.title is not None:
         upload_args.extend(['--title', options.title])
       message = (options.title or options.message or
                  CreateDescriptionFromLog(args))

third_party/upload.py

@@ -2440,6 +2440,7 @@ def RealMain(argv, data=None):
 
   # Process --message, --title and --file.
   message = options.message or ""
+  explicit_title = options.title is not None
   title = options.title or ""
   if options.file:
     if options.message:
@@ -2448,7 +2449,7 @@ def RealMain(argv, data=None):
     message = file.read()
     file.close()
   title = title or message.split('\n', 1)[0].strip()
-  if not title:
+  if not title and not explicit_title:
     if options.issue:
       prompt = "Title describing this patch set"
     else: