Heapq.merge suppreses IndexError from user generator #63218

assignee = 'https://github.com/rhettinger'
closed_at = <Date 2013-09-15.05:30:36.622>
created_at = <Date 2013-09-14.19:16:38.029>
labels = ['type-bug', 'library']
title = 'Heapq.merge suppreses IndexError from user generator'
updated_at = <Date 2013-09-15.05:30:36.622>
user = 'https://bugs.python.org/afn'

activity = <Date 2013-09-15.05:30:36.622>
actor = 'rhettinger'
assignee = 'rhettinger'
closed = True
closed_date = <Date 2013-09-15.05:30:36.622>
closer = 'rhettinger'
components = ['Library (Lib)']
creation = <Date 2013-09-14.19:16:38.029>
creator = 'afn'
dependencies = []
files = ['31760']
hgrepos = []
issue_num = 19018
keywords = ['patch']
message_count = 7.0
messages = ['197726', '197728', '197730', '197731', '197732', '197744', '197747']
nosy_count = 5.0
nosy_names = ['rhettinger', 'stutzbach', 'r.david.murray', 'python-dev', 'afn']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue19018'
versions = ['Python 2.7', 'Python 3.3']