[Sandbox] Fail to remove links / nodes in the live demo example

Describe the bug The sandbox example breaks when the user tries to remove an item by using the - links found in the editable Graph Data section. This applies to both nodes or links.

To Reproduce Steps to reproduce the behavior:

1. Go to the sandbox page
2. Expand the links or nodes property in the Graph Data section of the page
3. Click the - button next to the link / node that you wish to remove
4. See error

Expected behavior The selected node or link should dissappear from the editable data view and the graph shall be updated accordingly.

Additional context When trying to remove a link, the following error is displayed at the developer’s console:

react-dom.production.min.js?f6dd:188 TypeError: Cannot read property 'source' of null
    at eval (graph.helper.js?28ec:219)
    at Array.find (<anonymous>)
    at _loop (graph.helper.js?28ec:219)
    at _validateGraphData (graph.helper.js?28ec:216)
    at Object.initializeGraphState (graph.helper.js?28ec:324)
    at Graph.componentWillReceiveProps (Graph.jsx?fe1a:436)
    at sg (react-dom.production.min.js?f6dd:150)
    at Sg (react-dom.production.min.js?f6dd:178)
    at yh (react-dom.production.min.js?f6dd:202)
    at zh (react-dom.production.min.js?f6dd:203)

If the item you’re trying to delete is a node, then the following error is shown instead:

react-dom.production.min.js?f6dd:188 TypeError: Cannot read property 'x' of null
    at eval (Sandbox.jsx?dd0e:238)
    at Array.map (<anonymous>)
    at Sandbox.decorateGraphNodesWithInitialPositioning (Sandbox.jsx?dd0e:236)
    at Sandbox.render (Sandbox.jsx?dd0e:314)
    at Lg (react-dom.production.min.js?f6dd:167)
    at Sg (react-dom.production.min.js?f6dd:180)
    at yh (react-dom.production.min.js?f6dd:202)
    at zh (react-dom.production.min.js?f6dd:203)
    at Wh (react-dom.production.min.js?f6dd:212)
    at Zh (react-dom.production.min.js?f6dd:211)

[danielcaldas]

Fixed with #216

[oxyno-zeta]

Thanks 😃 Maybe the onDeltaUpdate (https://github.com/oxyno-zeta/react-editable-json-tree#ondeltaupdate) is better because there is a delta object that can help you to detect null objects and where are they no ?