`observable_add` doesn't raise any exception and just returns `None`

[sp35]

result = self.api.observable_add(value=obs_value)

This would just return None and there is no way I can catch the exception Couldn't guess observable type as it's just logged.

[eshaan7]

Reference code:

pyeti/pyeti/api.py

Line 684 in 5ec9da1

logging.error("An error occurred (%s): %s", resp.status_code, url)