Better nullability and error handling

[ZevEisenberg]

Checklist

• I've checked that all new and existing tests pass
• I've updated the documentation if necessary
• I've added an entry in the CHANGELOG to credit myself

Description

Fixes #290

Also does more idiomatic error handling:

Wrong:

NSError *error;
NSArray *result = [someObject someMethod error:&error];
if (!error) {
    // assume success
}

Correct:

NSError *error;
NSArray *result = [someObject someMethod error:&error];
if (result) {
    // assume success
}

Motivation and Context

The main motivation was addressing static analysis warnings I encountered when analyzing an Objective-C project. The error handling was just something I fixed along the way.

Note: I also added a couple of missing generics annotations which may affect the public interface. If they are imported into Swift, they will go from [Any] to [OHHTTPStubsDescriptor]. This is a breaking change for anyone who is using the output of this method in Swift. Actually, it may not be breaking, since in Swift, they were probably already doing something like for descriptor in descriptors as! [OHHTTPStubsDescriptor], and after this update, that line will throw a compile warning, not an error. So this can probably be a bugfix, not a major release.

Testing: I added a couple of missing tests for error throwing cases, and made sure all the tests were passing.

[AliSoftware]

Nice!

[AliSoftware]

Problem with this is, it's a reference type. So that means that users can't set stubDescriptors = newValue but they can [stubDescriptors append:…] though can't they?

[AliSoftware]

Oh wait it's in the private category so not exposed to the consumer is it? (Not easy to review from phone 😅)

[ZevEisenberg]

(Forgot to reply originally) copy never works on properties of NSMutableCopying type, because the setter calls -copy, which returns an immutable copy, i.e. an NSArray in this case. So you’d set a mutable array, and the value that gets stored would be immutable. Fun edge case in Obj-C land that should probably be a compile error.