ruby-on-rails - Ruby TypeErrorはDateをStringに変換できません

Question

私TypeError (can't convert Date into String)はRubyに入り、irbi testを使用して目的の値を取得できますが、redmineのグラフプラグイン内で上記のエラーが発生します。

Ruby のバージョンは 1.9.3p0 ですが、次のエラー ログが表示されます。

TypeError (can't convert Date into String):
plugins/redmine_graphs/app/controllers/graphs_controller.rb:130:in `parse'
plugins/redmine_graphs/app/controllers/graphs_controller.rb:130:in `block in issue_growth_graph'
plugins/redmine_graphs/app/controllers/graphs_controller.rb:126:in `each'
plugins/redmine_graphs/app/controllers/graphs_controller.rb:126:in `issue_growth_graph'
vendor/gems/ruby/1.9.1/gems/actionpack-3.2.8/lib/action_controller/metal
/implicit_render.rb:4:in `send_action'

別の質問として、Ruby のバージョンは 1.9.3p0 ですが、ログでは 1.91 になっています。なぜこのようなことが起こるのでしょうか?

redmine のグラフ プラグインの次のコードは、これを引き起こします。

# Displays projects by total issues over time
def issue_growth_graph

    # Initialize the graph
    graph = SVG::Graph::TimeSeries.new({
        :area_fill => true,
        :height => 300,
        :min_y_value => 0,
        :no_css => true,
        :show_x_guidelines => true,
        :scale_x_integers => true,
        :scale_y_integers => true,
        :show_data_points => false,
        :show_data_values => false,
        :stagger_x_labels => true,
        :style_sheet => "/plugin_assets/redmine-graphs-plugin/stylesheets/issue_growth.css",
        :width => 720,
        :x_label_format => "%Y-%m-%d"
    })

    # Get the top visible projects by issue count
    sql = "SELECT project_id, COUNT(*) as issue_count"
    sql << " FROM issues"
    sql << " LEFT JOIN #{Project.table_name} ON #{Issue.table_name}.project_id = #{Project.table_name}.id"
    sql << " WHERE (%s)" % Project.allowed_to_condition(User.current, :view_issues)
    unless @project.nil?
        sql << " AND (project_id = #{@project.id}"
        sql << "    OR project_id IN (%s)" % @project.descendants.active.visible.collect { |p| p.id }.join(',') unless @project.descendants.active.visible.empty?
        sql << " )"
    end 
    sql << " GROUP BY project_id"
    sql << " ORDER BY issue_count DESC"
    sql << " LIMIT 6"
    top_projects = ActiveRecord::Base.connection.select_all(sql).collect { |p| p["project_id"] }

    # Get the issues created per project, per day
    sql = "SELECT project_id, date(#{Issue.table_name}.created_on) as date, COUNT(*) as issue_count"
    sql << " FROM #{Issue.table_name}"
    sql << " WHERE project_id IN (%s)" % top_projects.compact.join(',')
    sql << " GROUP BY project_id, date"
    issue_counts = ActiveRecord::Base.connection.select_all(sql).group_by { |c| c["project_id"] }

    # Generate the created_on lines
    top_projects.each do |project_id, total_count|
        counts = issue_counts[project_id].sort { |a,b| a["date"]<=>b["date"] }         
        created_count = 0
        created_on_line = Hash.new
        #the place of error is following error
        created_on_line[(Date.parse(counts.first["date"])-1).to_s] = 0
        counts.each { |count| created_count += count["issue_count"].to_i; created_on_line[count["date"]] = created_count }
        created_on_line[Date.today.to_s] = created_count
        graph.add_data({
            :data => created_on_line.sort.flatten,
            :title => Project.find(project_id).to_s
        })
    end

    # Compile the graph
    headers["Content-Type"] = "image/svg+xml"
    send_data(graph.burn, :type => "image/svg+xml", :disposition => "inline")
end