commit f337050407872ef3cfba47033698061758e57762
author hellohuanlin <41930132+hellohuanlin@users.noreply.github.com> Wed Jul 05 22:42:19 2023 -0700
committer GitHub <noreply@github.com> Thu Jul 06 05:42:19 2023 +0000
tree 9a734605fa27830e62fce7cd764833c4283adc77
parent 61df84d1bdbd45c04b58e63c351b355227a6899e

[pigeon]fix a crash when casting NSNull to an Array (#4289)

Fixes a crash introduced in https://github.com/flutter/packages/pull/3658: 

```
static func fromList(_ list: [Any?]) -> NativeAuthSession? {
  if let userPoolTokensList = list[2] as! [Any?]? {}
}
```
where `list[2]` is `NSNull`, which is not an Optional, hence can't be casted to `[Any?]?`. 

Recall that `nilOrValue` helper is created for this purpose. So the fix is simply: 

```
static func fromList(_ list: [Any?]) -> NativeAuthSession? {
  if let userPoolTokensList: [Any?] = nilOrValue(list[2]) {} // <- HERE
}
```

## Why didn't we catch this regression

Missing unit tests - we did not test `NSNull` fields to ensure `nilOrValue` works for them.  

## Why did it work in previous version? 

It's surprising that this worked fine before! The original code is: 
```
static func fromList(_ list: [Any]) -> NativeAuthSession? {
  if let userPoolTokensList = list[2] as! [Any]? {}
}
```
From [my previous PR](https://github.com/flutter/flutter/issues/129283), we know that list[2] is an implicit optional (that contains a NSNull value). I think Swift made an exception here when casting implicit optional NSNull (either intentionally or unintentionally). 

*List which issues are fixed by this PR. You must list at least one issue.*

Fixes https://github.com/flutter/flutter/issues/129283

*If you had to change anything in the [flutter/tests] repo, include a link to the migration guide as per the [breaking change policy].*