Fix crash on invalid key path

[dcordero]

Fixed a crash when an invalid key path is indicated for a key in the JSONKeyPathsByPropertyKey method

[jspahrsummers]

It's a little hard to tell what this is fixing. From the test, am I correct in understanding that it fixes a crash when a nested key path is specified in +JSONKeyPathsByPropertyKey, but the JSON contains a primitive instead of an object at some part of that path?

If so, we should fix this by stepping through the JSON dictionary manually, not catching exceptions. Exceptions in Objective-C are generally used to indicate unrecoverable errors, so catching them is rarely safe. (Mantle does so as a convenience for release code, and the value of even that has been debated.)

[dcordero]

Yep it fix exactly that case. What exactly you mean with "stepping through the JSON dictionary manually" ? I mean, given the test case:

NSDictionary *values = @{
    @"username": @"foo",
    @"nested": @"bar",
    @"count": @"0"
    };

with a + JSONKeyPathsByPropertyKey like this:

+ (NSDictionary *)JSONKeyPathsByPropertyKey {
    return @{
        @"name": @"username",
        @"nestedName": @"nested.name",
        @"weakModel": NSNull.null,
    };
}

should we fill *error with a new error type an return nil from -(id)initWithJSONDictionary better than an Exception? or step over that key and continue with no error?

[jspahrsummers]

I mean that we shouldn't be executing code which will cause NSDictionary to throw an exception.

Instead, we should follow a generalized version of these steps:

1. Break apart nested.name into two components: nested and name
2. Retrieve nested from the dictionary. If it's not a dictionary itself, error out.
3. Retrieve name from the nested dictionary.

[dcordero]

Modified fix to avoid sending an exception an returning an error instead

[jspahrsummers]

Thank you! I made some minor formatting changes in df03aa9, but otherwise this looks great! 🌟