Steps to reproduce

1. create a file called test.py containing the following:

def frob(value=None): if value is not None: return -value return value

2. pylint test.py

Current behavior

pylint output contains E: 3,15: bad operand type for unary -: NoneType (invalid-unary-operand-type)

Expected behavior

There should be no invalid-unary-operator-type error for this line because it is not possible for value to be None here

pylint --version output

pete@dev:~$ pylint --version No config file found, using default configuration pylint 1.7.1, astroid 1.5.2 Python 2.7.6 (default, Oct 26 2016, 20:30:19) [GCC 4.8.4]