Raise UserError if summary is not given to `be commit`.

If the user doesn't provide the summary on the command line, through
stdin, or through editor_string, raise an error.  This will generally
happen with

  $ be commit
  (user doesn't enter any text in the editory)

1 files changed, 3 insertions, 0 deletions

diff --git a/libbe/command/commit.py b/libbe/command/commit.py
index 32ca3ef..8416107 100644
--- a/libbe/command/commit.py
+++ b/libbe/command/commit.py
@@ -84,6 +84,9 @@ class Commit (libbe.command.Command):
             body = libbe.util.encoding.get_file_contents(
                 params['body'], decode=True)
         if summary == None:  # use the first body line as the summary
+            if body == None:
+                raise libbe.command.UserError(
+                    'cannot commit without a summary')
             lines = body.splitlines()
             summary = lines[0]
             body = '\n'.join(lines[1:]).strip() + '\n'