sympy/sympy — pull request #2312 by skirpichev (2013-07-23 21:39:14+00:00)
Title: Fix issue 3744

The calculate_series in gruntz.py should always return a non-zero value for nontrivial expression. Let's do some cheap simplifications to check the result is not zero and call nseries() with increased n if it is.

This pull also add check for zero output in the Add._eval_as_leading_term()