Summary:
This PR attempts to fix issue https://github.com/facebook/react-native/issues/28278 and https://github.com/facebook/react-native/issues/29525
On Crashlytics, the following error occurs in file `RCTWebSocketModule.m` at method `-[RCTWebSocketModule webSocket:didFailWithError:]` when a nil value is inserted into a dictionary as a value.
```
Fatal Exception: NSInvalidArgumentException
*** -[__NSPlaceholderDictionary initWithObjects:forKeys:count:]: attempt to insert nil object from objects[0]
```
This PR is following the suggestion of this: https://github.com/facebook/react-native/issues/28278#issuecomment-597461650 and it replaces the values of any property if it is nil. In detail:
- it converts `error` to empty NSString if the original value is nil
- it converts `socketID` to a NSNumber object, which stores `-1` if the original value is nil
## Changelog
[iOS] [Fixed] - A crash in WebSocket module
Pull Request resolved: https://github.com/facebook/react-native/pull/30066
Test Plan: We were not able to reproduce the crash, but the report itself provided enough information to find a solution for this issue.
Reviewed By: shergin
Differential Revision: D24241147
Pulled By: sammy-SC
fbshipit-source-id: d5d632b49ca77b5d8be8b9c32358bef68f17d30a