Always return a string for StringUtil#cut_at_null_byte

[alex-quiterio]

I came across this strange behavior after reading the following open issue. Here's the stack trace with some insight:

1) FormatParser::MP3Parser decodes and estimates duration for a CBR MP3
     Failure/Error: value = tag.public_send(k)
     
     NoMethodError:
       undefined method `gsub' for nil:NilClass
     # /Users/code/libs/id3tag/lib/id3tag/frames/v2/genre_frame/genre_parser_pre_24.rb:25:in `just_genres'
     # /Users/code/libs/id3tag/lib/id3tag/frames/v2/genre_frame/genre_parser_pre_24.rb:12:in `genres'
     # /Users/code/libs/id3tag/lib/id3tag/frames/v2/genre_frame.rb:23:in `get_genres'
     # /Users/code/libs/id3tag/lib/id3tag/frames/v2/genre_frame.rb:8:in `genres'

The symptom:

The #initialize method of the class ID3Tag::Frames::V2::GenreFrame::GenreParser expects to get a string as a parameter but it can be invoked with nil instead.

Potential problem:

This scenario can happen due to the fact that StringUtil#cut_at_null_byte can return a value different than String. You can find one instance of the issue in D3Tag::Frames::V2::TextFrame

From the point of view of the StringUtil interface, I expect that cut_at_null_byte would cut the string until the first null_byte and return the first piece of the string. That happens in most of the cases but the edge case of "empty string" is still not covered.

Proposed solution:

In order to fix the issue and the symptoms, we just need to make sure #cut_at_null_byte returns always a String.

I've added some specs to the method StringUtil#cut_at_null_byte too.

Let me know if you have any questions or comments. I would be very happy to help :)
Thanks!

[krists]

@alex-quiterio Thanks for the detailed explanation. I completely agree that StringUtil#cut_at_null_byte should always return a string.

[krists]

@alex-quiterio I have released new version 0.10.1

[alex-quiterio]

@krists thanks a lot 🙇