Quite interesting. For a moment I've thought it is another JS issue but no. It's React who's strange https://github.com/facebook/react/blob/v0.11.2/src/browser/u... https://github.com/facebook/react/blob/v0.11.2/src/utils/tra...

Same behavior on Ruby:

    def content_markup(children)
      case children
      when String, Numeric
        children
      when NilClass, TrueClass, FalseClass
        return
      else
        # ...
      end
    end

    content_markup 'foo'
    #=> "foo"
    content_markup 0
    #=> 0
    content_markup true
    #=> nil
    content_markup false
    #=> nil
    content_markup nil
    #=> nil