Empty type can't be changed.

[chengxuncc]

I'm using #4017 simple type definition feature, so I can set type to empty. It will throw exception when I click Change Type.

Chrome console output:

react-dom.production.min.js:4408 TypeError: Cannot read property '0' of undefined
    at EditTypeModal.js:55
    at Array.reduce (<anonymous>)
    at hg (EditTypeModal.js:53)
    at Qi (react-dom.production.min.js:3274)
    at Ia (react-dom.production.min.js:3899)
    at Yo (react-dom.production.min.js:5514)
    at qo (react-dom.production.min.js:5536)
    at Rc (react-dom.production.min.js:5958)
    at Oc (react-dom.production.min.js:5925)
    at Lc (react-dom.production.min.js:6020)
uo @ react-dom.production.min.js:4408
n.callback @ react-dom.production.min.js:4773
no @ react-dom.production.min.js:4271
to @ react-dom.production.min.js:4259
Uo @ react-dom.production.min.js:4999
Go @ react-dom.production.min.js:5123
(anonymous) @ react-dom.production.min.js:5975
t.unstable_runWithPriority @ scheduler.production.min.js:274
xc @ react-dom.production.min.js:5974
Rc @ react-dom.production.min.js:5958
Oc @ react-dom.production.min.js:5925
Lc @ react-dom.production.min.js:6020
On @ react-dom.production.min.js:1737

EditTypeModal.js:55 Uncaught TypeError: Cannot read property '0' of undefined
    at EditTypeModal.js:55
    at Array.reduce (<anonymous>)
    at hg (EditTypeModal.js:53)
    at Qi (react-dom.production.min.js:3274)
    at Ia (react-dom.production.min.js:3899)
    at Yo (react-dom.production.min.js:5514)
    at qo (react-dom.production.min.js:5536)
    at Rc (react-dom.production.min.js:5958)
    at Oc (react-dom.production.min.js:5925)
    at Lc (react-dom.production.min.js:6020)
(anonymous) @ EditTypeModal.js:55
hg @ EditTypeModal.js:53
Qi @ react-dom.production.min.js:3274
Ia @ react-dom.production.min.js:3899
Yo @ react-dom.production.min.js:5514
qo @ react-dom.production.min.js:5536
Rc @ react-dom.production.min.js:5958
Oc @ react-dom.production.min.js:5925
Lc @ react-dom.production.min.js:6020
On @ react-dom.production.min.js:1737

[paulftw]

It's not yet clear how Ratel should be handling empty types since the feature hasn't been released yet and not clear what version it will be released in.
It shouldn't crash when empty types are there, full support shouldn't be too hard to implement