accept null from getContent

[cklab]

In response to issue #186

Return null from getContent to hide tooltip.

[wwayne]

Good catch, but typeof null === 'object', so I've sent another PR that can support both undefined and null. #202

Anyway, thanks for your suggestion and PR 👍

[cklab]

@wwayne That's correct, and that fact is exactly why this PR works. I'm confused as to your reasoning, this and #202 are accomplishing the same exact thing...

[wwayne]

For the same goal but not the exact thing, I dealt with getContent and children separately and worked with a new state which introduced from previous PR to control it so that it can cover more edge cases.

No offend, but for this PR

1.it can't deal with getContent={() => { return }}
2.it can't deal with <ReactTooltip>{}</ReactTooltip>
3.it doesn't work when working with delayHide, for example

<a data-for='custom-class' data-tip='hover on me will keep the tootlip'>(･ω´･ )</a>
<a data-for='custom-class' data-tip getContent={() => { return null }}>(･ω´･ )</a>
<ReactTooltip id='custom-class' class='extraClass' delayHide={1000} effect='solid'/>

4.I think we don't need to add typeof getContent !== 'undefined', I suppose if (getContent) is enough here