No error handling?

[virusman]

Is there any kind of error handling? i.e. when sending faxes with invalid phone numbers or other data, the API call would return the error message in previous versions of this gem. However, now it seems like it can only return a Reference with id or throw an unclear error, if anything goes wrong:

undefined method `start_with?' for nil:NilClass

[yujideveloper]

@virusman
This is same as #24, and fixed in #43.