Bar chart doesn't seem to cope gracefully with empty dataset

[mockdeep]

When I have an empty data set, I get an error from google charts:

 > Gchart.bar(:data => [[],[],[]])
NoMethodError: undefined method `-' for nil:NilClass
    from /home/fletch/.rvm/gems/ruby-2.1.2/gems/googlecharts-1.6.8/lib/gchart.rb:594:in `block in encode_scaled_dataset'
    from /home/fletch/.rvm/gems/ruby-2.1.2/gems/googlecharts-1.6.8/lib/gchart.rb:592:in `each'
    from /home/fletch/.rvm/gems/ruby-2.1.2/gems/googlecharts-1.6.8/lib/gchart.rb:592:in `encode_scaled_dataset'
    from /home/fletch/.rvm/gems/ruby-2.1.2/gems/googlecharts-1.6.8/lib/gchart.rb:624:in `simple_encoding'
    from /home/fletch/.rvm/gems/ruby-2.1.2/gems/googlecharts-1.6.8/lib/gchart.rb:328:in `set_data'
    from /home/fletch/.rvm/gems/ruby-2.1.2/gems/googlecharts-1.6.8/lib/gchart.rb:659:in `block in query_builder'
    from /home/fletch/.rvm/gems/ruby-2.1.2/gems/googlecharts-1.6.8/lib/gchart.rb:656:in `map'
    from /home/fletch/.rvm/gems/ruby-2.1.2/gems/googlecharts-1.6.8/lib/gchart.rb:656:in `query_builder'
    from /home/fletch/.rvm/gems/ruby-2.1.2/gems/googlecharts-1.6.8/lib/gchart.rb:652:in `url_builder'
    from /home/fletch/.rvm/gems/ruby-2.1.2/gems/googlecharts-1.6.8/lib/gchart.rb:299:in `url'
    from (eval):12:in `bar'
    from (irb):3

[kathgironpe]

@mockdeep shouldn't you be checking if data set is empty before using Gchart?

[mockdeep]

@katgironpe It doesn't seem like the role of the library to make that decision for users. If I pass an empty data set to the Google Charts API, it returns a blank graph, which is fine for my purposes. At the very least, a meaningful error message would be helpful.

[Chuongv]

So your expectation is that it returns an empty graph? Or an error?

[kathgironpe]

@mockdeep it's a rare case but agree about proper error handling.

[mockdeep]

I think the ideal situation for me would be for it just to return an empty graph. It's fairly common in the dev environment and in tests to have empty graphs, so it would be nice just to render it transparently instead of having to handle the error case.

[Seven0711]

请问使用Google chart要引入哪些文件，去哪里下载？