The __str__ method of the Mail class, doesn't actually return anything #292

Issue Summary

The __str__ method of the Mail class, doesn't actually return anything, hence trying something like logging.debug("Mail: %s\n", some_mail), where some_mail is an instance of the Mail class, will result in an exception.

Steps to Reproduce

1. Instantiate the Mail class
2. Print the instance

This will result in a TypeError exception:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-8-119834a39903> in <module>()
----> 1 print(message)

TypeError: __str__ returned non-string (type NoneType)

One possible fix would be to replace

    def __str__(self):
        self.get()

with

    def __str__(self):
        return str(self.get())

Technical details:

• sendgrid-python Version: master (latest commit: [bdba194])
• Python Version: 2.7