Crash with nil error parameter

[kristopherjohnson]

TBXML provides this method, which simply invokes another method with a nil error pointer:

- (id)initWithXMLData:(NSData*)aData {
    return [self initWithXMLData:aData error:nil];
}

There are other similar methods (-initWithXMLFile:, -initWithXMLFile:fileExtension:, etc.).

Unfortunately, if an error does occur, then the error handling code will try to dereference that nil pointer, and the app crashes. Some error-handling code does check for a null pointer before dereferencing it, but some does not.

Callers can work around this issue by calling the variant of the method that requires an error pointer. However, as-is these methods can easily lead to a crash, so I propose one of these actions be taken:

• Remove the methods that don't require an error parameter. Require callers to pass an error parameter.
• Change the methods that pass nil pointers such that they instead use a local error variable.
• Change the error-handling code so that it always checks for a null error before trying to dereference it.

[kristopherjohnson]

I have submitted a pull request with a fix. See #6