crashes when generate stats, is there any version requirement

git_stats generate -o stats 
git rev-list --pretty=format:'%h|%at|%ai|%aE' HEAD | grep -v commit
git shortlog -se HEAD
/Users/User/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/lib/git_stats/stats_view/charts/chart.rb:51:in `date_column_chart': undefined method `[]=' for nil:NilClass (NoMethodError)
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/lib/git_stats/stats_view/charts/activity_charts.rb:13:in `block in activity_by_date'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/lib/git_stats/stats_view/charts/chart.rb:13:in `initialize'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/lib/git_stats/stats_view/charts/activity_charts.rb:12:in `new'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/lib/git_stats/stats_view/charts/activity_charts.rb:12:in `activity_by_date'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/lib/git_stats/stats_view/charts/charts.rb:11:in `activity_by_date'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/templates/activity/_activity.haml:24:in `block in singletonclass'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/templates/activity/_activity.haml:65527:in `instance_eval'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/templates/activity/_activity.haml:65527:in `singletonclass'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/templates/activity/_activity.haml:65525:in `__tilt_70177236667600'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/tilt-1.4.1/lib/tilt/template.rb:170:in `call'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/tilt-1.4.1/lib/tilt/template.rb:170:in `evaluate'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/tilt-1.4.1/lib/tilt/haml.rb:24:in `evaluate'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/tilt-1.4.1/lib/tilt/template.rb:103:in `render'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/lib/git_stats/stats_view/template.rb:15:in `render'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/lib/git_stats/stats_view/view_data.rb:18:in `render_partial'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/templates/activity/by_date.haml:1:in `block in singletonclass'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/templates/activity/by_date.haml:65527:in `instance_eval'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/templates/activity/by_date.haml:65527:in `singletonclass'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/templates/activity/by_date.haml:65525:in `__tilt_70177236667600'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/tilt-1.4.1/lib/tilt/template.rb:170:in `call'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/tilt-1.4.1/lib/tilt/template.rb:170:in `evaluate'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/tilt-1.4.1/lib/tilt/haml.rb:24:in `evaluate'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/tilt-1.4.1/lib/tilt/template.rb:103:in `render'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/lib/git_stats/stats_view/template.rb:13:in `block in render'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/templates/layout.haml:29:in `block in singletonclass'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/templates/layout.haml:65527:in `instance_eval'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/templates/layout.haml:65527:in `singletonclass'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/templates/layout.haml:65525:in `__tilt_70177236667600'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/tilt-1.4.1/lib/tilt/template.rb:170:in `call'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/tilt-1.4.1/lib/tilt/template.rb:170:in `evaluate'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/tilt-1.4.1/lib/tilt/haml.rb:24:in `evaluate'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/tilt-1.4.1/lib/tilt/template.rb:103:in `render'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/lib/git_stats/stats_view/template.rb:13:in `render'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/lib/git_stats/stats_view/view.rb:15:in `block in render_all'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/lib/git_stats/stats_view/view.rb:14:in `each'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/lib/git_stats/stats_view/view.rb:14:in `render_all'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/lib/git_stats/generator.rb:5:in `render_all'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/lib/git_stats/cli.rb:15:in `generate'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/thor-0.18.1/lib/thor/command.rb:27:in `run'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/thor-0.18.1/lib/thor/invocation.rb:120:in `invoke_command'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/thor-0.18.1/lib/thor.rb:363:in `dispatch'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/thor-0.18.1/lib/thor/base.rb:439:in `start'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/gems/git_stats-1.0.9/bin/git_stats:10:in `<top (required)>'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/bin/git_stats:19:in `load'
	from /Users/charliewu/.rvm/gems/ruby-1.9.3-p194/bin/git_stats:19:in `<main>'