Markdown (and probably SyntaxHighlighter) default children value needs update

[radekwlsk]

With dcc 0.15.4 and:

The children property of dash_core_components.Markdown and dash_core_components.SyntaxHighlighter now accepts an array of strings (previously it had to be a string). Now, if an array is provided, it is collapsed into a string with line breaks (see #134).

now creating dcc.Markdown() component without any children value, for an empty component that will be later filled with a callback crashes in React constructor:

// must be a string or an array of strings
if(typeof props.children !== 'string') {
    props.children = props.children.join('\n');
}

as children is not a string, but the default children value that crashes on .join() call (at least that is what browser console tells me): TypeError: Cannot read property 'join' of null.

I think that the default value for dcc.Markdown.children should be "" or empty list.

Or if providing children value is required, then Python should catch components without it and raise an exception, as it is it was really hard to find the error.

[chriddyp]

Yeah, that typeof isn't strict enough, it should just be if (R.type(props.children) === 'Array'). I'll fix this one.

[chriddyp]

Thanks for reporting!